Thermoplastic liquid crystal polymer film, circuit board, and methods respectively for manufacturing said film and said circuit board

ABSTRACT

Provided are a thermoplastic liquid crystal polymer film having an improved thermo-adhesive property, a circuit board, and methods respectively for producing the same. The thermoplastic liquid crystal polymer film has a segment orientation ratio SOR of 0.8 to 1.4 and a moisture content of 300 ppm or less. The circuit board contains a plurality of circuit board materials wherein the circuit board materials are at least one member selected from the group consisting of an insulating substrate having a conductor layer on at least one surface, a bonding sheet, and a coverlay. At least one of the circuit board materials includes a thermoplastic liquid crystal polymer film. The circuit board shows a solder heat resistance when the circuit board is placed in a solder bath at 290° C. for 60 seconds in accordance with JIS C 5012.

CROSS REFERENCE TO THE RELATED APPLICATION

This application is a continuation application, under 35 U.S.C. §111(a), of international application No. PCT/JP2014/075875, filed Sep.29, 2014, which claims priority to Japanese patent applications No.2013-208209 filed Oct. 3, 2013, No. 2014-065751 filed Mar. 27, 2014, andNo. 2014-119850 filed Jun. 10, 2014, the entire disclosures of which areherein incorporated by reference as a part of this application.

FIELD OF THE INVENTION

The present invention relates to a film of a thermoplastic liquidcrystal polymer capable of forming an optically anisotropic melt phase(hereinafter may be referred to as a thermoplastic liquid crystalpolymer film, or TLCP film, or simply abbreviated as a liquid crystalpolymer film, or LCP film) having an improved thermo-adhesive property,and a method for producing the same, and to a circuit board and a methodfor producing the same.

BACKGROUND ART

Electronics such as information processing devices and communicationequipment generally include circuit boards inside. A circuit boardtypically includes an insulating-material substrate and aconductive-material layer on the substrate, and the conductive-materiallayer includes circuits to form a predetermined circuit pattern. Variouselectronic components can be mounted on the circuit board by means ofprocessing such as soldering. Recently a multilayer circuit board havinga plurality of conductor layers has come to be widely used.

There has been known a conventional circuit board including a polyimideas an insulating material, for example, a circuit board that comprises(i) a wiring substrate comprising a polyimide film and a circuit formedfrom a conductor layer on the polyimide film and (ii) a coverlaycomprising a polyimide film and an adhesive layer to be bonded to thewiring substrate.

However, such a circuit board sometimes has poor heat resistance,especially poor solder heat resistance, due to usage of an adhesive.Further, some circuit boards contain residual solvent originated fromthe adhesive. The presence of the solvent in the circuit boards maycause defects in the circuit board after multi-layering process,resulting in deterioration of reliability of the circuit boards.Accordingly, a technique for forming a circuit board without using anadhesive has been desired.

In recent years, there have been remarkable developments in the field ofinformation processing, such as personal computers, as well as in thefield communication equipment, such as mobile phones. Such electronicsand communication equipment have come to be operated at higherfrequencies of gigahertz region. In the high frequency band, however, itis known that the electronics and communication equipment generally haveincreased in transmission loss.

Circuit boards have been conventionally known as one comprising a wiringsubstrate in which a conductor circuit is formed on a polyimide film,and a coverlay film bonded on the wiring substrate, the coverlay filmcomprising a polyimide film and an adhesive layer.

However, such a circuit board sometimes has poor heat resistance,especially poor solder heat resistance, due to adhesive usage. Further,some circuit boards contain residual solvent originated from theadhesive. The presence of the solvent in the circuit boards may causedefects in the circuit board after multi-layering process, resulting indeterioration of reliability of the circuit boards. Accordingly, atechnique for forming a circuit board without using an adhesive has beendesired.

On the other hand, TLCP films have attracted attention as substratematerials for forming circuit boards without using an adhesive. The TLCPfilm, however, contains rigid skin layers on the surfaces, the skinlayers generated during extrusion. Where the TLCP films are heat-bondedwith each other, the skin layers sometimes interrupt sufficientinterlayer adhesion between the TLCP films.

In order to improve adhesive property, for example, Patent Document 1(JP Laid-open Patent Publication No. 2010-103269) discloses a method forproducing a multilayer circuit board including: extruding athermoplastic liquid crystal polymer (TLCP) capable of forming anoptically anisotropic melt phase to form a TLCP film, softening at leastone surface of the TLCP film by physical grinding or UV radiation torender the film surface to have a hardness of 0.01 to 0.1 GPa measuredin accordance with the nanoindentation method so as to form an adhesivesurface, and counterposing the adhesive surface on a circuit surface ofa wiring substrate comprising a conductor circuit on at least onesurface of a TLCP film capable of forming an optically anisotropic meltphase and carrying out a thermo-compression bonding of the entirecomponents.

In the meanwhile, where a circuit board is produced without usage of anadhesive by laminating a conductor layer of a metal such as copper to bebonded to a LCP layer, a process for accomplishing an improved peelstrength (strength against peeling) has been carried out by forming anuneven surface on the conductor layer to enhance compressive adhesionbetween the conductor layer and the insulating layer by an anchoringeffect of the uneven surface. The optimization of the uneven structurehas been studied.

For example, Patent Document 2 (WO 2012/020818) discloses a metal-cladlaminate having a metal foil on one or both surfaces of a liquid crystalpolymer layer, wherein the metal foil has projections on a surface layerportion on a side to be in contact with the LCP layer, the projectionbeing formed by roughening the metal foil surface; the projections havean aspect ratio (H/L) of a projection height H with respect to aprojection bottom width L in a range of 3 to 20; the projection heightis in a range of 0.1 to 2 μm; and the LCP layer has a thickness of 10 to2000 μm and a thickness tolerance of less than 6%.

SUMMARY OF THE INVENTION

Patent Document 1 achieves the enhanced interlayer adhesion betweenliquid crystal polymer films by carrying out the softening treatment ofthe skin layers by physical polishing or ultraviolet radiation. PatentDocument 1, however, fails to disclose or suggest improvement ininterlayer adhesion between liquid crystal polymer films without causingdamage to the skin layer.

Patent Document 2 describes that the roughening treatment of the metalfoil improves interlayer adhesion between the liquid crystal polymerfilm and the metal foil, but does not recognize improvement ininterlayer adhesion between liquid crystal polymer films by carrying outa specific treatment on the liquid crystal polymer films. Further, theinvention described in this document has not been studied disadvantagescaused by existence of projections on the metal foil against the liquidcrystal polymer.

An object of the present invention is to provide a liquid crystalpolymer film having an improved thermo-adhesive property and makingpossible to improve interlayer adhesion between the film and anadherend, and a method producing the same.

Another object of the present invention is to provide a circuit boardhaving an improved interlayer adhesion and a method producing the same.

Based on the result of intensive studies to achieve the above objects,the inventors of the present invention have found the following aspectsof the present invention.

That is, a first aspect of the present invention relates to a method forproducing a TLCP film at least including:

preparing a TLCP film being capable of forming an optical anisotropicmelt phase and having a segment orientation ratio SOR of 0.8 to 1.4,degassing the TLCP film by degassing the film (i) under vacuum of 1500Pa or lower for 30 minutes or more, and/or by degassing the film (ii)under heating at a temperature ranging from 100° C. to 200° C., andthereby producing a TLCP film having a segment orientation ratio SOR of0.8 to 1.4 and a moisture content of 300 ppm or less.

In the above production method, the degassing process may include:

a first degassing of the TLCP film by heating the prepared TLCP filmunder heating at a temperature ranging from 100° C. to 200° C. for apredetermined period of time, and

a second degassing of the first-degassed TLCP film by further degassingthe TLCP film after the first degassing under vacuum of 1500 Pa or lowerfor a predetermined period of time. Preferably, the degassing undervacuum (i) or the second degassing process may be carried out underheating the film at a temperature ranging from 80° C. to 200° C. undervacuum of 1500 Pa or lower.

Further, the TLCP film to be subjected to degassing may be preferably inroll form.

A second aspect of the present invention embraces a TLCP film having animproved thermo-adhesive property (thermo-adhesion-improved TLCP film).Such a TLCP film has a segment orientation ratio SOR of 0.8 to 1.4 and amoisture content of 300 ppm or less. Further, the TLCP film may have afilm thickness of about 10 to 200 μm. The TLCP film may be produced bythe above-described production method. The TLCP film may be a TLCP filmwrapped with a packaging material having a gas barrier property(gas-barrier packaging material).

It should be noted that the present invention might embrace a packagedTLCP film product comprising a TLCP film having thermo-adhesive propertyand a packaging material having gas barrier property.

In the packaging structure, the gas barrier packaging material may havean oxygen permeability of, for example, 10 mL/m²·day·MPa or less.Further, the gas barrier packaging material may have a moisturepermeability of, for example, 10 g/m²/day or less.

A third aspect of the present invention relates to a method forproducing a circuit board at least including:

preparing a plurality of circuit board materials;

stacking the prepared circuit board materials in accordance with apredetermined structure of a circuit board to obtain a stacked material,followed by conducting thermo-compression bonding of the stackedmaterial by heating the stacked material under a predeterminedcompression pressure; wherein

the prepared circuit board materials are at least one member selectedfrom the group consisting of an insulating substrate having a conductorlayer on at least one surface, a bonding sheet, and a coverlay, and

(I) at least one of the prepared circuit board materials comprises adegassed TLCP film having an improved thermo-adhesive property, the TLCPfilm being subjected to degassing as recited above and/or

(II) at least one of the prepared circuit board materials comprises anon-degassed TLCP film, and the degassing process as recited above isconducted after the preparation of the circuit board materials andbefore the thermo-compression bonding.

In the production method, at least one of the circuit board materialsmay comprise a TLCP film having an improved thermo-adhesive property.

In the production method, among the circuit board materials selectedfrom the group consisting of an insulating substrate, a bonding sheet,and a coverlay, at least two circuit board materials may comprise afirst LCP film having a higher melting point and higher heat resistanceand a second LCP film having a lower melting point and lower heatresistance than the first LCP film. The difference in melting pointbetween the first and second LCP films may be within 70° C.

In the method for producing the circuit board, the thermo-compressionbonding process may include a thermo-compression bonding conducted undera compression pressure of 5 MPa or lower (preferably 0.5 to 2.5 MPa).For example, the circuit board materials may be subjected tothermo-compression bonding by heating the materials at a temperatureranging from (Tm−60)° C. to (Tm+40)° C., where Tm is the melting pointof the TLCP film subjected to the thermo-compression bonding.

A fourth aspect of the present invention embraces a circuit boardcomprising a plurality of circuit board materials, wherein:

the circuit board materials are at least one member selected from thegroup consisting of an insulating substrate having a conductor layer onat least one surface, a bonding sheet, and a coverlay;

at least one of the circuit board materials comprises a TLCP film; and

the circuit board shows a solder heat resistance when the circuit boardis placed in a solder bath at a temperature of 290° C. for 60 seconds inaccordance with a method of JIS C 5012. The circuit board may be acircuit board produced by the above-described production method.

Preferably, the circuit board may have a bonding strength between theTLCP film and a circuit board material in contact with the TLCP film, ina value measured in accordance with JIS C5016-1994, of

0.8 kN/m or higher where the circuit board material is an insulatingsubstrate material (e.g., TLCP film), or

0.3 kN/m or higher where the circuit board material is a conductorlayer.

It should be noted that where circuit board material has a conductivematerial portion, bonding strength is determined depending on thesurface area ratio of the conductive material portion in contact withthe TLCP film. The surface area ratio may be determined as existingratio of conductive material as follows:

$\begin{matrix}{{Existin}\; g\mspace{11mu} {ratio}} \\{{of}\mspace{14mu} {conductive}\mspace{14mu} {material}}\end{matrix} = {{\begin{pmatrix}{{Surface}\mspace{14mu} {area}\mspace{14mu} {of}\mspace{14mu} {circuit}\mspace{20mu} {patterns}\mspace{14mu} {on}} \\{{circuit}\mspace{14mu} {board}\mspace{14mu} {unit}\mspace{14mu} {in}\mspace{14mu} {contact}\mspace{14mu} {with}\mspace{14mu} {the}\mspace{14mu} {target}\mspace{14mu} {LCP}\mspace{14mu} {film}}\end{pmatrix}/\begin{pmatrix}{{Surface}\mspace{14mu} {area}\mspace{14mu} {of}\mspace{14mu} {entire}} \\{{circuit}\mspace{14mu} {board}\mspace{14mu} {unit}}\end{pmatrix}} \times 100}$

Where the ratio is 30% or more, the bonding strength is measured as abonding strength between the LCP film and a conductor layer. Where theratio is less than 30%, the bonding strength is measured as a bondingstrength between the LCP film and an insulating substrate material.

Preferably, the circuit board may have a favorably isotropic bondingstrength. For example, where the TLCP film and the circuit boardmaterial are peeled off along a first direction (A direction) or along asecond direction (B direction) perpendicular to the first direction tomeasure the bonding strength between the TLCP film and the circuit boardmaterial in accordance with JIS C5016-1994,

the minimum value of bonding strength in four directions of a forward Adirection, an adverse A direction, a forward B direction, and an adverseB direction may be:

(i) 0.5 kN/m or higher where the circuit board material is an insulatingsubstrate material, or

(ii) 0.25 kN/m or higher where the circuit board material is a conductorlayer.

In the circuit board, at least two circuit board materials may be TLCPfilms. In the circuit board, a conductor layer may be interposed betweena first TLCP film and a second TLCP film. The difference in meltingpoint between the first TLCP film and the second TLCP film may be in arange from 0° C. to 70° C.

All of the circuit board materials selected from the group consisting ofan insulating substrate, a bonding sheet, and a coverlay may compriseTLCP films. An insulating substrate may be bonded to another insulatingsubstrate without a bonding sheet. An insulating substrate may be bondedto a coverlay without a bonding sheet.

Preferably, the circuit board may have a conductor layer with a smoothsurface. For example, at least one surface of the conductor layer mayhave a surface roughness (Rz_(JIS)) of 1.25 μm or less as an averagevalue of ten-points measured according to a method conforming toISO4287-1997.

As an indicator to show reduction in thickness of the circuit board, forexample, a circuit board may have (n+1) layers of TLCP film layers and nlayers of conductor circuit layers, each of the conductor circuit layerbeing interposed between TLCP film layers. In this case, the circuitboard may comprise TLCP films to be adhered with each other in a stateinterposing the conductor circuit layers without using a bonding sheet.

An L2/L1 ratio may be used as an indication of the degree of subductionof the circuit board, where L1 denotes the thickness of the insulatingsubstrate portion at which the conductor circuit is not formed, and L2denotes the thickness of the insulating substrate portion at which theconductor circuit is formed. Where the subduction of the conductorcircuit in the circuit board is suppressed, the L2/L1 ratio inpercentage may be from 80 to 100%.

The circuit board may be a circuit board comprising a conductor circuithaving a strip line structure or a micro-strip line structure.

The present invention may encompass a circuit board produced by theabove-described production method. The circuit board of the presentinvention may be either a single-layer circuit board having one layer ofconductor layer or a multi-layer circuit board having a plurality ofconductor layers as described above.

The present invention, as another aspect, may also encompass inventionsas described below.

A fifth aspect of the present invention may be a method of producing acircuit board, the method comprising:

preparing at least one unit circuit board and at least one TLCP film asa circuit board material to be adhered to the unit circuit board,

the unit circuit board comprising a TLCP film and a conductor layerformed on one or the both surfaces of the thermoplastic liquid crystalpolymer film, and

the circuit board material being adhered to the surface of the conductorlayer;

performing a first degassing of the unit circuit board(s) and thecircuit board material(s) under heating at a temperature ranging from100° C. to 200° C. for a predetermined period of time, for example,under the ambient pressure;

performing a second degassing the of the unit circuit board(s) and thecircuit board material(s) under vacuum of 1500 Pa or lower;

performing integration of a stacked material formed by stacking the atleast one circuit board material and the at least one unit circuit boardby thermo-compression bonding by application of heat and pressure to thestacked material,

wherein the surface of the conductor layer in contact with the circuitboard material has a surface roughness (Rz_(JIS)) of 1.25 μm or less asan average value of ten-points measured according to a method conformingto ISO 4287-1997.

The second degassing may be carried out at a temperature in a range from80° C. to 200° C. The second degassing may be performed substantiallywithout applying compression pressure. The circuit board material may beat least one selected from the group consisting of a bonding sheet and acoverlay.

Also, the preparation process of the unit circuit board may comprise:

thermo-compression bonding of a metal foil(s) to a TLCP film on one orboth surfaces of the TLCP film; and

forming an oxidation-resistant coat on the metal surface of thethermo-compressed metal foil(s).

The conductor layer may preferably include a copper layer made of acopper foil. The conductor layer may preferably include an alloy layercontaining copper as an oxidation-resistant coating.

The preparation process of the unit circuit board may further compriseapplying a silane-coupling agent on the conductor layer surface.

A sixth aspect of the present invention may be a circuit board producedby the above method.

In the sixth aspect of the present invention, the circuit board may be acircuit board comprising one or more unit circuit boards and one or morecircuit board materials to be bonded to the unit circuit board(s),wherein

-   -   at least one of the unit circuit boards comprises a TLCP film        and a conductor layer(s) formed on one or both sides of the TLCP        film surface, the conductor layer(s) having a surface roughness        (Rz_(JIS)) of 1.25 μm or less as an average value of ten points        measured in accordance with ISO 4287-1997 on the surface bonded        to the circuit board material,    -   at least one of the circuit board materials comprises a TLCP        film, and    -   the circuit board shows a solder heat resistance when the        circuit board is placed in a solder bath at a temperature of        290° C. for 60 seconds in accordance with the method conforming        to JIS C 5012.

According to the first aspect of the present invention, a specificdegassing process can improve thermo-adhesive property of a TLCP film,while maintaining an isotropic property of the TLCP film. As a result,even without an adhesive agent, interlayer adhesion of the circuit boardcomprising a LCP film(s) can be enhanced.

Further, by packing the TLCP film subjected to a specific degassingprocess with a gas barrier packaging material, the TLCP film can betransported or conveyed as a packaged product containing the TLCP filmwhile maintaining a degassed condition.

According to the method for producing the TLCP film according to thesecond aspect, the TLCP film having improved adhesion property can beefficiently produced.

The circuit board according to the third aspect of the present inventioncan suppress local adhesion failure by enhancing the interlayer adhesiveproperty of the circuit board even using a TLCP film(s). The circuitboard can inhibit occurrence of blisters on the circuit board during ahigh temperature treatment such as a reflow process for mountingelectronic components on the circuit board. Further, interlayer adhesionwithout adhesive usage enables to enhance reliability of the circuitboard.

According to the fourth aspect of the present invention, a method forproducing a circuit board can achieve production of such a circuit boardin an efficient way.

BRIEF DESCRIPTION OF THE DRAWINGS

In any event, the present invention will become more clearly understoodfrom the following description of preferred embodiments thereof, whentaken in conjunction with the accompanying drawings. However, theembodiments and the drawings are given only for the purpose ofillustration and explanation, and are not to be taken as limiting thescope of the present invention in any way whatsoever, which scope is tobe determined by the appended claims, and:

FIG. 1 is a schematic cross-sectional view for illustrating a shape ofthe rolled material formed of a TLCP film according to one embodiment ofthe present invention;

FIGS. 2A and 2B are schematic cross-sectional views for explaining aproduction process of a circuit board according to an embodiment of thepresent invention, and show states before and after lamination,respectively;

FIGS. 3A and 3B are schematic cross-sectional views for explaining aproduction process of a circuit board according to another embodiment ofthe present invention, and show states before and after lamination,respectively;

FIG. 4 is a schematic cross-sectional view for explaining a structure ofone embodiment of the present invention comprising n layers of theconductor layers and (n+1) layers of the insulating layer containing theconductor layers inside;

FIG. 5A is a schematic cross-sectional view showing a laminatecomprising a conductor circuit and two sheets of liquid crystal polymerfilm sandwiching the conductor circuit for explaining a subductionamount of the conductor layer into the circuit board according to anembodiment of the present invention;

FIG. 5B is a schematic cross-sectional view showing a laminate furthercomprising a ground conductor on both surfaces of the laminate of FIG.5A in the circuit board according to an embodiment of the presentinvention; and

FIGS. 6A, 6B and 6C show cross sectional SEM images of Examples 4 and 5and Comparative Example 4, respectively. Scale width in the image is 100μm, and the SEM images have the same magnification with each other.

DESCRIPTION OF EMBODIMENTS

The first aspect of the present invention is based on the findings asdescribed below. That is, (i) TLCP films have the highest level of gasbarrier properties among various organic materials, probably because ofhaving a rigid mesogenic groups. This is a great advantage of TLCP filmsin comparison with other organic materials. Accordingly, the necessityof degassing of TLCP films has never been conceived in the past. (ii)However, for reasons that are uncertain, the presence of gasifiablecomponents such as moisture contained in thermoplastic liquid crystalpolymer, and/or moisture adsorbed on the surface of the TLCP film and/orair existing on the surface of the TLCP film may cause deterioration ininterlayer adhesion between the film and an adherend, and it has beenassumed that such gasifiable components may cause blisters in thecircuit board provided with the TLCP film at a high temperature. (iii)Based on the above assumption, the inventors of the present inventionhave found that where a specific degassing process is carried out to aTLCP film, surprisingly, the degassed TLCP film can achieve improvedadhesive property with maintaining isotropic property of the film so asto enhance interlayer adhesion between the film and an adherend as wellas to suppress the occurrence of blisters on the circuit board evenexposed to a high temperature condition.

Production Method of TLCP Film

One embodiment of the present invention is a method for producing a TLCPfilm, the method at least includes:

preparing a TLCP film being capable of forming an optical anisotropicmelt phase and having a segment orientation ratio SOR of 0.8 to 1.4, and

degassing the TLCP film by degassing the TLCP film (i) under vacuum of1500 Pa or lower for 30 minutes or more, and/or by degassing the TLCPfilm (ii) under heating at a temperature ranging from 100° C. to 200°C., so as to produce a TLCP film having a segment orientation ratio SORof 0.8 to 1.4 and a moisture content of 300 ppm or less.

Preparation Step of TLCP Film

The TLCP film to be prepared is formed from a melt-processable liquidcrystalline polymer. In particular, chemical formulation of thethermoplastic liquid crystal polymer is not particularly limited to aspecific one as long as it is a liquid crystalline polymer that can bemelt-processable, and examples thereof may include a thermoplasticliquid crystal polyester, or a thermoplastic liquid crystal polyesteramide obtained by introducing an amide bond thereto.

Furthermore, the thermoplastic liquid crystal polymer may be a polymerobtained by further introducing, to an aromatic polyester or an aromaticpolyester amide, an imide bond, a carbonate bond, a carbodiimide bond,or an isocyanate-derived bond such as an isocyanurate bond.

Specific examples of the thermoplastic liquid crystal polymer used inthe present invention may include known thermoplastic liquid crystalpolyesters and thermoplastic liquid crystal polyester amides obtainedfrom compounds classified as (1) to (4) as exemplified in the following,and derivatives thereof. However, it is needless to say that, in orderto form a polymer capable of forming an optically anisotropic meltphase, there is a suitable range regarding the combination of variousraw-material compounds.

(1) Aromatic or Aliphatic Dihydroxy Compounds (See Table 1 forRepresentative Examples)

TABLE 1 Chemical structural formulae of representative examples ofaromatic or aliphatic dihydroxyl compounds

HO(CH₂)_(n)OH n is an integer of 2 to 12

(2) Aromatic or Aliphatic Dicarboxylic Acids (See Table 2 forRepresentative Examples)

TABLE 2 Chemical structural formulae of representative examples ofaromatic or aliphatic dicarboxylic acids

HOOC(CH₂)_(n)COOH n is an integer of 2 to 12

(3) Aromatic Hydroxycarboxylic Acids (See Table 3 for RepresentativeExamples)

TABLE 3 Chemical structural formulae of representative examples ofaromatic or aliphatic hydroxycarboxylic acids

(4) Aromatic Diamines, Aromatic Hydroxy Amines, and AromaticAminocarboxylic Acids See Table 4 for Representative Examples)

TABLE 4 Chemical structural formulae of representative examples ofaromatic diamines, aromatic hydroxy amines, or aromatic aminocarboxylicacids

Representative examples of liquid crystal polymers obtained from theseraw-material compounds may include copolymers having structural unitsshown in Tables 5 and 6.

TABLE 5 Representative examples (1) of a thermoplastic liquid crystalpolymer

(A)

(B)

(C)

(D)

(E)

(F)

TABLE 6 Representative examples (2) of thermoplastic liquid crystalpolymer

(G)

(H)

(I)

(J)

Of these copolymers, polymers including at least p-hydroxybenzoic acidand/or 6-hydroxy-2-naphthoic acid as repeating units are preferable; andparticularly preferred polymers include:

a polymer (i) having repeating units of p-hydroxybenzoic acid and6-hydroxy-2-naphthoic acid, and

a polymer (ii) having repeating units of

-   -   at least one aromatic hydroxycarboxylic acid selected from a        group consisting of p-hydroxybenzoic acid and        6-hydroxy-2-naphthoic acid,    -   at least one aromatic diol selected from a group consisting of        4,4′-dihydroxybiphenyl and hydroquinone, and    -   at least one aromatic dicarboxylic acid selected from a group        consisting of terephthalic acid, isophthalic acid, and        2,6-naphthalene dicarboxylic acid.

For example, in the case where the polymer (i) comprises a thermoplasticliquid crystal polymer having repeating units of at leastp-hydroxybenzoic acid (A) and 6-hydroxy-2-naphthoic acid (B), the liquidcrystal polymer may have a mole ratio (A)/(B) of preferably about(A)/(B)=10/90 to 90/10, more preferably about (A)/(B)=50/50 to 85/15,and further preferably about (A)/(B)=60/40 to 80/20.

Furthermore, in the case where the polymer (ii) comprises a liquidcrystal polymer having repeating units of at least one aromatichydroxycarboxylic acid (C) selected from a group consisting ofp-hydroxybenzoic acid and 6-hydroxy-2-naphthoic acid, at least onearomatic diol (D) selected from a group consisting of4,4′-dihydroxybiphenyl and hydroquinone, and at least one aromaticdicarboxylic acid (E) selected from a group consisting of terephthalicacid, isophthalic acid, 2,6-naphthalene dicarboxylic acid, the liquidcrystal polymer may have a mole ratio of aromatic hydroxycarboxylic acid(C):aromatic diol (D):aromatic dicarboxylic acid (E)=30 to 80:35 to10:35 to 10, more preferably about (C):(D):(E)=35 to 75:32.5 to12.5:32.5 to 12.5, and further preferably about (C):(D):(E)=40 to 70:30to 15:30 to 15.

Furthermore, the liquid crystal polymer may have a mole ratio of arepeating structural unit derived from an aromatic dicarboxylic acidrelative to a repeating structural unit derived from an aromatic diol ofpreferably (D)/(E)=95/100 to 100/95. Deviation from this range may tendto result in a low degree of polymerization and deterioration inmechanical strength.

It should be noted that, in the present invention, optical anisotropy ina molten state can be determined by, for example, placing a sample on ahot stage, heating the sample with an elevating temperature undernitrogen atmosphere, and observing light transmitted through the sample.

Preferred thermoplastic liquid crystal polymer has a melting point(hereinafter, referred to as Tm₀) in a range from 260° C. to 360° C.,and more preferably from 270° C. to 350° C. The melting point isdetermined by measuring the temperature at which the main endothermicpeak appears using a differential scanning calorimeter (ShimadzuCorporation DSC).

As long as the advantageous effect of the present invention is notdeteriorated, to the thermoplastic liquid crystal polymer, may be addedany thermoplastic polymer such as a polyethylene terephthalate, amodified polyethylene terephthalate, a polyolefin, a polycarbonate, apolyarylate, a polyamide, a polyphenylene sulfide, a polyether etherketone, and a fluorine resin; and/or various additives. If necessary, afiller may be added to the thermoplastic liquid crystal polymer.

The TLCP film used in the present invention can be obtained by extrudinga thermoplastic liquid crystal polymer. As long as the direction ofrigid rod-like molecules of the thermoplastic liquid crystal polymer canbe controlled, any extrusion method may be applied. In particular,well-known methods such as a T-die method, a laminate-stretching method,and an inflation method (tubular blown film extrusion method) areindustrially advantageous. In particular, the inflation method or thelaminate-stretching method can apply stresses not only in a machinedirection of the film (or the machine processing direction, hereinafterreferred to as MD direction), but also in a transverse direction(hereinafter, abbreviated as TD direction) perpendicular to the MDdirection. Accordingly, the inflation method or the laminate-stretchingmethod can be advantageously used to obtain a film having controlledproperties such as molecular orientation and dielectric characteristicsin both the MD and TD directions.

The extrusion molding is preferably accompanied by a stretchingtreatment in order to control the orientation. For example, in theextrusion molding using a T-die method, a molten polymer sheet extrudedfrom a T-die may be stretched in the MD direction and the TD directionat the same time, alternatively a molten polymer sheet extruded from aT-die may be stretched in sequence, first in the MD direction and thenthe TD direction.

Also, in the extrusion molding using an inflation method, a tubularsheet being melt-extruded from an annular die may be drawn with apredetermined draw ratio (corresponding to a stretching ratio in the MDdirection) and a predetermined blow ratio (corresponding to a stretchingratio in the TD direction).

The stretching ratios carried out in such extrusion molding may be, as astretching ratio in the MD direction (or draw ratio), for example, about1.0 to 10, preferably about 1.2 to 7, and more preferably 1.3 to 7;and/or as a stretching ratio in the TD direction (or blow ratio), forexample, about 1.5 to 20, preferably 2 to about 15, and still morepreferably about 2.5 to 14.

The ratio of the TD direction-stretching ratio relative to the MDdirection-stretching ratio (TD direction/MD direction), may be, forexample, 2.6 or less, preferably about 0.4 to 2.5.

If necessary, the extrusion-molded TLCP film may be subjected to furtherstretching. The stretching method itself is known, and either biaxialstretching or uniaxial stretching may be employed. From the viewpoint ofeasy control of molecular orientation, biaxial stretching is preferable.The stretching may be carried out using a known machine such as auniaxial stretching machine, a simultaneous biaxial stretching machine,and a sequential biaxial stretching machine.

If necessary, a known or conventional heat treatment may be carried outin order to control a melting point and/or thermal expansion coefficientof the TLCP film. Heat treatment conditions can be set appropriatelydepending on the purpose. The heat treatment may be carried out byheating for hours at a temperature of, for example, (Tm₀−10)° C. orhigher, wherein Tm₀ denotes a melting point of a liquid crystal polymer,for example, about (Tm₀−10)° C. to (Tm₀+30)° C., and preferably aboutTm₀° C. to (Tm₀+20)° C. to increase a melting point (Tm) of the TLCPfilm.

Thus-obtained TLCP film according to the present invention has improvedproperties such as dielectric properties, gas barrier properties and lowmoisture absorption, thus the TLCP film can be suitably used as acircuit board material.

In view of desired heat resistance and processability of the film, themelting point (Tm) of the TLCP film may be selected in a range fromabout 200° C. to 400° C., preferably about 250° C. to 360° C., morepreferably about 260° C. to 350° C. (for example, 260° C. to 340° C.).It should be noted that the melting point of the film can be determinedby observing the thermal behavior of the film using a differentialscanning calorimeter. That is, a test film is heated at a rate of 20°C./min to completely melt the film, and the melt is rapidly cooled orquenched to 50° C. at a rate of 50° C./min. Subsequently, the quenchedmaterial is reheated at a heating rate of 20° C./min., and a position ofan endothermic peak appearing in the reheating process may be recordedas a melting point of the film.

The TLCP film used in the present invention may have any thickness.Where the TLCP film is used in a high-frequency transmission line, theTLCP film may have a thickness as thick as possible because usage of athicker film can reduce transmission loss. Where a TLCP film is used asan electrically insulating layer, the film may preferably have athickness in a range from 10 to 500 μm, and more preferably in a rangefrom 15 to 200 μm. Since a film having too small thickness has smallrigidity and poor strength, it is possible to achieve a desiredthickness by laminating the films having a thickness in a range from 10to 200 μm.

Degassing Process

Thus-obtained TLCP films are subjected to a degassing process forremoving air or moisture present in and/or on the film.

Degassing process may be carried out in the production of a TLCP filmhaving improved thermo-adhesiveness, and/or may be carried out as one ofthe processes during the production of a circuit board.

Degassing process enables to improve the thermo-adhesiveness of the TLCPfilm, and also enables to enhance interlayer adhesion between the TLCPfilm and an adherend.

The TLCP film subjected to the degassing process may have any shape aslong as degassing of the TLCP film is possible. For example, in thedegassing process, the TLCP film may be prepared as a sheet materialthat may be provided with a conductor layer; as a multi-layer laminate(for example, a multi-layer laminate comprising a plurality of filmlayers each of which may be provided with a conductor layer); or as aproduct in roll form.

For example, where a product in roll form is used, the product in rollform may be prepared by winding a film onto a tubular core in a known orconventional manner. FIG. 1 is a schematic view for explaining a productin roll form comprising a TLCP film. As shown in FIG. 1, a rolledproduct 1 is formed by winding a TLCP film 3 onto a tubular core 2.

The product in roll form, for example, as shown in FIG. 1, may have awinding thickness (W) of 1000 mm or smaller, for example, about 10 to900 mm, preferably 800 mm or smaller, and more preferably 600 mm orsmaller.

The degassing of the TLCP film can be carried out by degassing the TLCPfilm under a certain vacuum condition (for example, a vacuum drying)and/or degassing under heat condition (for example, a heat drying) toreduce air and moisture on and/or in the TLCP film to an extremely lowlevel. As a result, surprisingly, the TLCP film that has undergone sucha degassing process can improve the thermo-adhesive property.

For example, although the present invention does not exclude thesoftening process, such TLCP films can achieve enhanced adhesiveproperty even without softening treatment such as destruction of theskin layer in the TLCP film. If desired, a surface treatment such assoftening treatment may be carried out for TLCP films.

In the degassing process, degassing of the TLCP film can be carried out(i) by degassing under vacuum of 1500 Pa or lower for 30 minutes ormore, and/or (ii) by degassing under heating at a temperature rangingfrom 100° C. to 200° C.

The degassing process may be carried out in a condition satisfyingeither degassing (i) under vacuum, or degassing (ii) under heating,preferably in a condition satisfying both (i) and (ii).

The degassing condition where both (i) and (ii) are satisfied may be acondition where both (i) and (ii) are satisfied at the same time, i.e.,degassing a TLCP film by heating at a specific temperature under aspecific vacuum degree (vacuum pressure). Alternatively, the degassingcondition where both (i) and (ii) are satisfied may be a condition where(i) and (ii) are carried out separately, i.e., degassing a TLCP film inthe order of from (i) to (ii) or in the order of from (ii) to (i).

It should be noted that where degassing process (i) and (ii) are carriedout separately, another process might be inserted within a range notadversely affecting the film, between the degassing (i) and (ii) orbetween the degassing (ii) and (i).

Moreover, from the viewpoint of improving degassing efficacy, degassingmay be carried out without substantial pressurization (under pressurerelease). For example, degassing may be carried out under a minimumpressure or pressure-released state (for example, under a compressionpressure of about 0 to 0.7 MPa, preferably under a compression pressureof about 0 to 0.5 MPa).

Degassing under vacuum (i) may be carried out at a vacuum degree of 1500Pa or lower, preferably 1300 Pa or lower, and more preferably 1100 Pa orlower.

Where degassing under vacuum is performed independently, degassing maybe carried out at an ambient temperature (for example, from 10° C. to50° C., preferably from 15° C. to 45° C.). In view of enhancing thedegassing efficiency, degassing may be carried out under heating, forexample, at a heating temperature ranging from 50° C. to 200° C. (forexample, from 50° C. to 150° C.), preferably from 80° C. to 200° C., andmore preferably from about 90° C. to about 190° C.

Degassing under heating (ii) may be carried out in a range from 100° C.to 200° C., preferably from 105° C. to 190° C., and more preferably from110° C. to 180° C.

Degassing temperature under heating may be set in a predeterminedtemperature range with respect to a melting point (Tm) of the TLCP film.Degassing may be carried out by heating at a temperature ranging from(Tm−235)° C. to (Tm−50)° C. [e.g., from (Tm−200)° C. to (Tm−50)° C.],preferably, from (Tm−225)° C. to (Tm−60)° C. [e.g., from (Tm−190)° C. to(Tm−60)° C.], and more preferably from (Tm−215)° C. to (Tm−70)° C.[e.g., from (Tm−180)° C. to (Tm−70)° C.].

By heating the TLCP film in a specific temperature range as describedabove, while suppressing rapid moisture generation from the film, themoisture in the film (for example, inside or on a surface of the film)can be degassed as water vapor, or the air on the surface of the filmcan be degassed by enhancing kinetic energy of the air.

It should be noted that where degassing under heating is carried outindependently, the degassing might be carried out under a condition thatdoes not contain the vacuum condition of 1500 Pa or lower. For example,degassing may be carried out by heating under an atmospheric pressure(or ambient pressure) where the pressure is not specifically adjusted.Alternatively, if necessary, degassing may be carried out by heatingunder a reduced pressure from the atmospheric pressure (for example,beyond 1500 Pa and less than 100000 Pa, preferably about 3000 to 50000Pa).

The period of time required for degassing procedure may be suitably setdepending on various conditions such as a state of the TLCP film, avacuum degree, and/or a heating temperature. In view of removingmoisture and air from the entire TLCP film, the period for degassing forthe degassing process (i) and/or the degassing process (ii) (i.e., undervacuum, under heating, under vacuum while heating) may be same ordifferent. The degassing period may be 30 minutes or more, 40 minutes ormore, or 50 minutes or more. The degassing period may be 6 hours orless, 4 hours or less, 3 hours or less, 2 hours or less, or 1.5 hours orless.

Alternatively, the degassing period may be set appropriately dependingon the moisture content in the TLCP film, for example, may be carriedout until the TLCP film has a desired moisture content range to bedescribed later (for example, 300 ppm or less, or 200 ppm or less).

As described above, where degassing under vacuum (i) and degassing underheating (ii) are carried out in combination to the extent thatthermo-adhesiveness of the TLCP film is capable of being increased, thedegassing processes (i) and (ii) may be carried out in any order,preferably carried out by degassing under heating (ii) as a firstdegassing, followed by degassing under vacuum (i) as a second degassing.

Specifically, for example, degassing process may comprise a firstdegassing process in which degassing of the circuit board materials iscarried out under heating at a temperature ranging from 100° C. to 200°C. for a predetermined time, and a second degassing process in whichdegassing of the circuit board materials is carried out under vacuum of1500 Pa or lower for another predetermined time. These degassingprocesses may be appropriately carried out by combining theabove-mentioned conditions.

TLCP Film Having Improved Thermo-Adhesiveness

By carrying out such a degassing process, surprisingly, a TLCP filmhaving enhanced thermo-adhesive property can be obtained. Although thereason for this achievement is not clear, the following mechanism ispresumed. Since the TLCP film is excellent in gas barrier property,there is a possibility that the TLCP film itself may suppress escape ofmoisture from the film once the moisture is contained inside, as well asmay suppress escape of air from the film where the TLCP film absorbs theair on the surface.

Further, there is another possibility described as follows. The maincomponent of the gas released from the resin is water vapor in general.The water vapor volume becomes several thousand times when water isconverted to vapor. In the meantime, as the vacuum status proceeds,moisture can be hardly released from inside of the film after reachingequilibrium of the emission amount from the resin and the emissionamount of the vacuum pump. Accordingly, where thermo-compression bondingis carried out under vacuum, the water molecules contained inside of thefilm may be hardly released.

Where the film itself is a source for generating the air and themoisture, local adhesion failure (local delamination) between bondedlayers may occur due to the air and the moisture remained in the film oron the surface of the film in the lamination process for the circuitboard production.

Further, the TLCP film obtained by a specific degassing method canachieve an extremely low moisture content while maintaining isotropicproperty of the polymer.

The TLCP film obtained by the degassing process has a SegmentOrientation Ratio SOR of 0.8 to 1.4, and a moisture content of 300 ppmor less.

The moisture content may be preferably 200 ppm or less, more preferably180 ppm or less, and even more preferably 150 ppm or less. Here, themoisture content indicates a value measured by the method described inExamples below.

The Segment Orientation Ratio SOR as an indicator of isotropic propertyof the film is 0.8 to 1.4, and may be preferably 0.9 to 1.3, morepreferably 1.0 to 1.2, and particularly preferably 1.0 to 1.1.

Here, the Segment Orientation Ratio SOR is an index descriptive of adegree of molecular orientation, and represents, unlike the standard MOR(Molecular Orientation Ratio), a value that takes the thickness of anobject into consideration.

Since the film is isotropic, the film may preferably have a dimensionalstability in the MD and TD directions of within ±1%, more preferablywithin ±0.5%, and more preferably within ±0.1%. Here, the dimensionalstability may be a value measured in accordance with IPC-TM-6502.2.4.

The obtained TLCP film may be used as an insulating substrate layer of aunit circuit board comprising a conductor layer formed on one or bothsides of the insulating substrate layer. Alternatively, the TLCP filmmay be used as an adhesive material (for example, a bonding sheet and acoverlay) for bonding to a conductor layer(s).

The TLCP film may have a dielectric loss tangent at 25 GHz of, forexample, 0.0025 or less (e.g., about 0.0001 to 0.0023), and preferablyabout 0.0010 to 0.0022. The TLCP film having such a dielectric losstangent enables to lower power consumption as well as to reduce noise.

The relative dielectric constant of the TLCP film varies depending onthe thickness of the film. The TLCP film may have a relative dielectricconstant at 25 GHz in the TD direction, for example, of 3.25 or less(e.g., about 1.8 to 3.23), and preferably about 2.5 to 3.20. It shouldbe noted that the dielectric constant can be generally calculated bymultiplying the vacuum dielectric constant (=8.855×10⁻¹² (F/m)) torelative dielectric constant.

For example, the dielectric constant measurement may be carried out by aresonance perturbation method at a frequency of 10 GHz. Where a 1 GHzcavity resonator (manufactured by Kanto Electronic Application andDevelopment Inc.) is connected to a network analyzer (“E8362B”,manufactured by Agilent Technologies, Inc.), and a small sample (width:2.7 mm×length: 45 mm) is inserted into the cavity resonator, thedielectric constant and the dielectric loss tangent of the sample can bemeasured from the change in resonance frequency before and afterinserting the material to expose the material to an environment at atemperature of 20° C. and a humidity of 65% (RH) for 96 hours.

The present invention may also embrace a packaged TLCP film product. Thepackaged TLCP film product may comprise the TLCP film havingthermo-adhesive property and a gas barrier packaging material packingthe TLCP film inside. In this case, the TLCP film is packed with thepackaging material having a gas barrier property.

The packaged TLCP film product makes it possible to transport or conveya degassed TLCP film with maintaining the degassed state since the TLCPfilm is packed with a gas barrier packaging material.

The shape of the TLCP film may be any shape such as a sheet material asdescribed above, a multilayer laminate, and a product in roll form(rolled product). If necessary, a conductor layer or a conductive layermay be formed on the TLCP film.

From the viewpoint of portability, the TLCP film to be packed in thepackaged product may be preferably in roll form.

The gas barrier packaging material may have, for example, a moisturepermeability of 10 g/m²/day or less (e.g., 0.5 to 10 g/m/day),preferably 8 g/m²/day or less, and more preferably 6 g/m²/day or less.

Furthermore, the gas barrier packaging material may have, for example,an oxygen permeability of 10 mL/m²/day/MPa or less (for example 0.5 to10 mL/m²/day/MPa), preferably 8 mL/m²/day/MPa or less, and morepreferably 5 mL/m²/day/MPa or less.

As the gas barrier packaging material, there may be exemplified variousgas barrier films, and a laminate of a gas barrier film with a CLAF, apaper, and/or a non-woven fabric.

Examples of the gas barrier films may include various types of filmssuch as an aluminum foil-laminated film, an aluminum-evaporated film, asilica-evaporated film, a polyvinylidene chloride-coated film and othergas barrier films. The gas barrier film may have a substrate film suchas a polyester film, a polyethylene film, and a polypropylene film.

Furthermore, the outside of these films and/or laminates may be furtherpacked with a paper or others; and/or these films and/or laminates maybe housed in a carton box, a crate, a metal case, a pedestal and others.

Method for Producing Circuit Board

As one embodiment of the present invention, there may be mentioned amethod for producing a circuit board having an improved interlayeradhesion even without an adhesive agent.

The producing method at least includes:

preparing a plurality of circuit board materials;

stacking the prepared circuit board materials in accordance with apredetermined structure of a circuit board to obtain a stacked material,followed by conducting thermo-compression bonding of the stackedmaterial by heating under a predetermined compression pressure; wherein

the prepared circuit board materials are at least one member selectedfrom the group consisting of an insulating substrate having a conductorlayer (e.g., a conductor circuit or a conductor pattern, a conductorfoil, a conductor film) on at least one surface, a bonding sheet, and acoverlay, and

(I) at least one of the prepared circuit board materials comprises adegassed thermoplastic liquid crystal polymer film subjected to theabove-mentioned degassing, and/or

(II) at least one of the prepared circuit board materials comprises anon-degassed thermoplastic liquid crystal polymer film, and theabove-mentioned degassing process is conducted after the preparation ofthe circuit board materials and before the thermo-compression bonding.

That is, in the method for producing a circuit board of the presentinvention, the interlayer adhesion of the circuit board can be improvedby carrying out the following process (I) and/or process (II).

In the process (I), a degassed TLCP film is prepared as a TLCP film in apreparation process.

In the process (II), a specific degassing process to degas a TLCP filmis carried out after preparation of the circuit board materials andbefore thermo-compression bonding.

Preparation of Circuit Board Materials

In the preparation process, a plurality of circuit board materials (orinsulating substrate materials), are prepared. The circuit boardmaterials can comprise at least one member selected from the groupconsisting of an insulating substrate, a bonding sheet, and a coverlay,where the insulating substrate having a conductor layer (e.g., aconductor circuit or a conductor pattern, a conductor foil, a conductorfilm) on at least one surface.

In the preparation, the prepared circuit board materials may be, forexample, a plurality of insulating substrates each having a conductorlayer on at least one surface; alternatively, may be a combination of(i) an insulating substrate having a conductor circuit on at least onesurface and (ii) at least one circuit board material selected from thegroup consisting of a bonding sheet and a coverlay.

As described above, in the process (I), at least one member selectedfrom the group consisting of an insulating substrate, a bonding sheet,and coverlay may comprise a degassed TLCP film having an improvedthermo-adhesiveness. By using such a TLCP film having an improvedthermo-adhesiveness; it is possible to improve the interlayer adhesionof the circuit board even carrying out a conventional thermo-compressionbonding process for producing a circuit board.

As the insulating substrate, there may be mentioned various organicmaterials and inorganic materials used in the conventional circuitboard. Examples of the organic materials may include a thermoplasticliquid crystal polymer, a polyimide, a cycloolefin polymer, a fluorineresin, an epoxy resin, a phenolic resin and an acrylic resin, and otherorganic materials. Examples of the inorganic materials may include aceramic, and the like. These materials may be used in the circuit boardsingly or in combination of two or more. Of these, from the viewpoint ofhigh-frequency characteristics and dimensional stability, the TLCPinsulating substrate is preferred.

Examples of the insulating substrates each having a conductor layer onat least one surface may include:

a unit circuit board comprising an insulating substrate and a conductorcircuit or pattern formed on one surface of the insulating substrate;

a unit circuit board comprising an insulating substrate and conductorcircuits or patterns formed on both surfaces of the insulatingsubstrate;

a unit circuit board comprising an insulating substrate, a conductorcircuit or pattern formed on one surface of the insulating substrate,and a conductor film or foil formed on the other surface of theinsulating substrate;

a conductor-clad laminate comprising an insulating substrate and aconductor film or foil formed on one surface of the insulatingsubstrate; and

a conductor-clad laminate comprising an insulating substrate andconductor films or foils formed on both surfaces of the insulatingsubstrate.

Conductor Layer

The conductor layer can be at least formed for example from a conductivemetal. By using a known circuit processing method, the conductor layermay be formed into any pattern of circuits. As the conductor for forminga conductor layer, there may be mentioned various metals havingconductivity, such as gold, silver, copper, iron, nickel, aluminum, andan alloy metal thereof.

Any known method may be used as a method for forming a conductor layeron an insulating substrate of a TLCP film. For example, a metal layermay be formed by evaporation, electroless plating, and/or electrolyticplating. Alternatively, a metal foil (for example, copper foil) may bethermo-compression bonded on the surface of the TLCP film.

The metal foil constituting the conductor layer may be preferably ametal foil used in electrical connections. Examples of the metal foilsmay include a copper foil, as well as various metal foils such as gold,silver, nickel, aluminum foils, and also an alloy foil comprising thesemetals in a substantial manner (for example, 98% by weight or greater).

Of these metal foils, a copper foil can be preferably used. The speciesof the copper foil is not particularly limited, and can be any of copperfoil usable in the circuit board, for example, a rolled copper foil oran electrolytic copper foil.

From the viewpoint of improvement in solder heat resistance andinterlayer adhesion, it is preferable that the conductor layer has asmooth surface.

Preferably, the conductor layer may have a surface roughness (Rz_(JIS))of 1.25 μm or less, preferably 1.2 μm or less, and more preferably 1.15μm or less as an average value of ten-points measured according to amethod conforming to ISO4287-1997. The lower limit of Rz_(JIS) is notparticularly limited, and for example, may be about 0.5 μm.

The conductor layer may have an arithmetic mean roughness of, forexample, 0.15 μm or less, or 0.14 μm or less measured according to themethod conforming to ISO4287-1997 (Ra). The lower limit of Ra is notparticularly limited, and for example, may be about 0.05 μm, or may beabout 0.11 μm.

In the above configuration, it may be possible for a conductive layer onthe TLCP film to have a smooth surface even where the conductive layeris not adhered to another layer in the lamination for obtaining alaminate. It should be noted that where the conductor layer is processedinto circuits, it might be sufficient for the remained part of theconductor layer (i.e., circuit part) to have a smooth surface.

The conductor layer may preferably have a thickness of, for example, 1to 50 μm (e.g., about 5 to 50 μm), and more preferably of 8 to 35 m(e.g., 10 to 35 μm).

The conductor layer may contain an oxidation-resistant coat on thesurface. The surface treatment of the conductor layer makes it possibleto form an alloy layer on the surface of the conductor layer, the alloylayer having a higher oxidation resistance than the conductor layer bodyitself. The conductor layer having such an oxidation-resistant coat canadvantageously prevent deterioration of the conductor layer due tooxidation of the conductor surface during the degassing process. It isalso expected to achieve a further improvement in adhesion due to thealloy layer.

For example, the preparation process of the unit circuit board maycomprise:

thermo-compression bonding of a metal foil(s) to a TLCP film on one orboth surfaces of the TLCP film; and

forming an oxidation-resistant coat on the surface of the metal foil(s).

The preparation process of the unit circuit board may further includeapplying or attaching a silane-coupling agent on the conductor layersurface.

As the oxidation-resistant coat, there may be exemplified anoxidation-resistant alloy layer, an oxidation-resistant plating layer,an anticorrosive agent layer such as a benzotriazole-coating layer, andother oxidation-resistant layer.

It should be noted that depending on the type of the conductor layersand oxidation resistant coat, the oxidation-resistant coat might beformed either before or after processing circuits.

For example, if the conductor layer comprises a thermo-compressionbonded metal foil, the oxidation-resistant alloy layer may be preferablyformed from an alloy metal including at least the metal constituting themetal foil in order to enhance adhesive property. For example, where themetal foil constituting the conductor layer is a copper foil, an alloylayer may be an alloy at least containing copper. For example, anoxidation-resistant alloy layer may be preferably formed beforeprocessing circuits.

For example, such an alloy layer may be formed using “FatBOND GT”manufactured by MEC Co., Ltd.

It should be noted that, there might be an alloy portion existing apartfrom the copper foil, the alloy portion containing no copper. Such analloy portion without copper may be etched with an etching liquid. Assuch an etching solution, there may be used, for example “MEC REMOVERS-651A” (produced by MEC Co., Ltd.), “S-BACK H-150” (produced by SASAKICHEMICAL CO., LTD.), an aqueous solution containing an inorganic acidsuch as nitric acid, and the like.

From the viewpoint of improving adhesive property of the conductorlayer, a known or conventional silane-coupling agent may be applied orattached to the surface of the conductor layer (in particular the alloylayer). Application of the silane-coupling agent to the alloy layersurface can further improve bonding strength between the conductor layerand the TLCP film. Even without forming uneven surface exerting ananchoring effect on the surface of the conductor layer, it is possibleto achieve a bonding strength indicated by a high peel strength by thethermo-compression while maintaining the smooth surface of the conductorlayer in the thermo-compression bonding.

Bonding Sheet and/or Coverlay

As an adhesive circuit board material used for adhering to the conductorlayer, one or more circuit board materials (adhesive materials) may beprepared in addition to the unit circuit board. The adhesive materialmay be preferably a TLCP film. Examples of the adhesive materials mayinclude at least one selected from a bonding sheet and a coverlay. Itshould be noted that the coverlay is typically used to cover theconductor layer as an outermost layer, and that the bonding sheet istypically used to bond the circuit board materials. The bonding sheetand/or the coverlay may be composed of a TLCP film. Preferably, at leastone selected from the bonding sheet and the coverlay may be composed ofa TLCP film having an improved thermo-adhesive property.

For example, where a TLCP film subjected to degassing process isreferred to as an adhesion-improved LCP film, and a TLCP film notsubjected to degassing process is referred to as an un-degassed LCPfilm, a combination of suitable circuit board materials may beexemplified as follows:

(a) a circuit board including an un-degassed LCP film as an insulatingsubstrate and an adhesion-improved LCP film as a bonding sheet, andoptionally an un-degassed LCP film as a coverlay;

(b) a circuit board including an un-degassed LCP film as an insulatingsubstrate and an adhesion-improved LCP film as a bonding sheet, andoptionally an adhesion-improved LCP film as a coverlay;

(c) a circuit board including an adhesion-improved LCP film as aninsulating substrate and an un-degassed LCP film as a bonding sheet, andoptionally an un-degassed LCP film as a coverlay;

(d) a circuit board including an adhesion-improved LCP film as aninsulating substrate and an adhesion-improved LCP film as a bondingsheet, and optionally an un-degassed LCP film as a coverlay;

(e) a circuit board including an adhesion-improved LCP film as aninsulating substrate and an adhesion-improved LCP film as a bondingsheet, and optionally an adhesion-improved LCP film as a coverlay;

(f) a circuit board including an adhesion-improved LCP film as aninsulating substrate and an un-degassed LCP film as a coverlay;

(g) a circuit board including an un-degassed LCP film as an insulatingsubstrate and an adhesion-improved LCP film as a coverlay;

(h) a circuit board including an adhesion-improved LCP film as aninsulating substrate and an adhesion-improved LCP film as a coverlay;

(i) a circuit board including an adhesion-improved LCP film as a firstinsulating substrate, an adhesion-improved LCP film as a secondinsulating substrate, and optionally an un-degassed LCP film as acoverlay;

(j) a circuit board including an adhesion-improved LCP film as a firstinsulating substrate, an adhesion-improved LCP film as a secondinsulating substrate, and optionally an adhesion-improved LCP film as acoverlay; and other combinations.

Where the degassing process is carried out in the producing process ofthe circuit board, since the specific degassing process provides LCPfilms with improved thermo-adhesive property, an un-degassed LCP filmcan be used as any of the prepared the circuit board material such as aninsulating substrate, a bonding sheet, and a coverlay.

In the circuit board comprising the circuit board materials, the circuitboard materials may comprise at least two TLCP films including a firstTLCP film and a second TLCP film, wherein a conductor layer isinterposed between the first TLCP film and the second TLCP film. In sucha case, the difference in melting point between the first TLCP film andthe second TLCP film may be in a range of, for example, 0° C. to 70° C.,and preferably about 0° C. to 60° C. (for example, about 10° C. to 50°C.).

For example, the first LCP film may be a high-melting-point LCP filmhaving higher heat resistance, and the second LCP film may be alow-melting-point LCP film having lower heat resistance than the firstLCP film. For example, at least two circuit board materials selectedfrom an insulating substrate, a bonding sheet and a coverlay maycomprise a combination of a high-melting-point LCP film having higherheat resistance (for example, melting point of about 300° C. to 350° C.)and a low-melting-point LCP film having lower heat resistance (forexample, melting point of about 250° C. to 300° C.).

Further, since the circuit board according to the present invention isexcellent in interlayer adhesion, for example, the circuit boardmaterials adhered to each other may be composed of high-melting-pointLCP films, alternatively may be composed of low-melting-point LCP films.In this case, the difference in melting point between high-melting-pointLCP films or between low-melting-point LCP films may be, for example,about 0° C. to 20° C., and preferably about 0° C. to 10° C.

Alternatively, the adjacent circuit board materials adhered to eachother may comprise a combination of a high-melting-point LCP film and alow-melting-point LCP film. In this case, the difference in meltingpoint between LCP films may be, for example, exceeding 20° C., andpreferably 30° C. to 70° C.

The adhesion-improved LCP film can be used as the high-melting-point LCPfilm or can be used as the low-melting-point LCP film. Among theadjacent LCP films adhered to each other (for example, a combination ofa high-melting-point LCP film and a high-melting-point LCP film, acombination of a low-melting-point LCP film and a low-melting-point LCPfilm, a combination of a high-melting-point LCP film and alow-melting-point LCP film), at least one LCP film in the combinationmay be an adhesion-improved LCP film; preferably both of the LCP filmsin the combination may be adhesion-improved LCP films. Alternatively, atleast the low-melting-point LCP film in the combination may be anadhesion-improved LCP film.

Depending on the configuration of the circuit board, the melting pointof the LCP film used as an adhesive material may be identical to themelting point of the substrate of the unit circuit board. Alternatively,the LCP film used as an adhesive material may have a lower melting pointthan a LCP film constituting the unit circuit board. In that case, thedifference in melting point between the LCP films may be, for example,about 0° C. to 70° C., and more preferably about 0° C. to 60° C.

It should be noted that within the range that does not impair theeffects of the present invention, the surface treatment might beperformed on the circuit board material (in particular on the LCP film).The surface treatment can be carried out, for example, by known methodssuch as ultraviolet irradiation, plasma irradiation, and physicalpolishing.

Degassing Process

By carrying out the above-mentioned degassing process in the productionmethod of a circuit board, the TLCP film may have improved adhesiveness.

The degassing process in the production method may be carried out beforethe thermo-compression bonding process, or after the preparation processand before the thermo-compression bonding process.

Where the degassing process is carried out in the method for producing acircuit board, preferably the degassing process may comprise:

a first degassing of the circuit board materials under heating at atemperature ranging from 100° C. to 200° C. for a predetermined time;and

a second degassing of the circuit board materials under vacuum of 1500Pa or lower for another predetermined time.

Furthermore, degassing process may be carried out as a pre-heatingprocess prior to the thermo-compression bonding. The pre-heating processmay be carried out, for example, in a heating temperature range from 50°C. to 150° C. under vacuum of 1500 Pa or lower. The heating temperatureduring the pre-heating process may be preferably about 60° C. to 120°C., and more preferably 70° C. to 110° C.

Such a pre-heating process makes it possible to remove air and/ormoisture on and/or in the LCP film to some extent, even if anun-degassed film is used as the circuit board materials. As a result, itis possible to improve the interlayer adhesion between the LCP film andan adherend even without an adhesive agent.

The pre-heating process may be carried out under a vacuum degree of 1500Pa or less, preferably 1300 Pa or less, and more preferably 1100 Pa orless.

During the pre-heating process, a compression pressure may be applied tothe circuit board material within a range that does not inhibit theeffect of the invention. The compression pressure in the pre-heatingprocess may be, for example, 0.8 MPa or less, and more preferably 0.6MPa or less. The pre-heating process may be preferably carried out withapplying a compression pressure as low as possible, preferablysubstantially without applying a compression pressure.

The pre-heating process may be carried out, for example, for about 30 to120 minutes, preferably about 40 to 100 minutes, and more preferablyabout 45 to 75 minutes.

For example, where the first degassing process is combined with thesecond degassing process, the degassing process may be carried out asfollows:

First Degassing Process: Degassing Under Heating

In order to avoid gas discharge in the lamination process for producinga circuit board or post-process thereafter, degassing can be carriedout. Without degassing process, a gaseous compound may be dischargedfrom LCP films used for a circuit board material or adhesive material,as well as from metal layer of the conductor layer. The degassingprocess may be carried out by preliminarily degassing a unit circuitboard(s) as well as a LCP film(s) used for the adhesive material underheating, for example, at atmospheric pressure (or ambient pressure).

The heating may be carried out at a temperature ranging from 100° C. to200° C., preferably of 110° C. to 190° C. The heating time can beadjusted appropriately depending on the heating temperature, and may be,for example, 30 minutes to 4 hours, and preferably 1 hour to 3 hours.

The degassing under heating may be conducted under conditions that donot contain a vacuum degree of 1500 Pa or less, for example, may becarried out under an atmospheric pressure (or normal pressure) withoutadjusting the pressure. If desired, the degassing under heating may beconducted under a pressure reduced from the atmospheric pressure (e.g.,beyond 1500 Pa and less than 100000 Pa, preferably about 3000 to 50000Pa).

Incidentally, in order to prevent oxidation of conductors (such ascopper foil); it is preferable to heat under an inert gas atmospheresuch as nitrogen in the first degassing process. Alternatively, such aheating may be carried out in the state that the conductor has anoxidation-resistant coat (e.g., oxidation-resistant alloy layer,oxidation resistant plating layer, anti-rust inhibitor layer such asbenzotriazole-coated layer) on the surface.

Second Degassing Process: Enhanced or Intensified Degassing

Subsequently, further degassing of LCP films used for the unit circuitboard and the adhesive material may be preferably carried out undervacuum. This degassing process (second degassing process) may beperformed at a vacuum degree of 1500 Pa or less, preferably 1300 Pa orless, and more preferably 1100 Pa or less. The degassing period can beadjusted appropriately according to the vacuum degree, for example 30minutes or more, 40 minutes or more, or 50 minutes or more. Thedegassing period may be 6 hours or less, 4 hours or less, and 3 hours orless, 2 hours or less, or 1.5 hours or less.

The degassing under vacuum may be carried out at an ambient temperature(e.g., in a range from 10° C. to 50° C., preferably 15° C. to 45° C.),alternatively may be carried out under heating in view of increasingdegassing efficiency. Where heating the LCP films, the heatingtemperature may be in a range from 80° C. to 200° C., preferably 100° C.to 200° C., and more preferably 115° C. to 200° C. As described above,by heating the LCP film at a certain temperature lower than the meltingpoint of the film, it is possible to carry out degassing water in thefilm as the water vapor while suppressing the rapid moisture generationfrom the film.

The second degassing process, from the viewpoint of improving thedegassing, may be carried out substantially without pressurization(carried out under pressure release). For example, where a circuit boardis produced using a vacuum hot press apparatus; a unit circuit board(s)and a LCP film(s) for an adhesive material(s) are degassed in the firstdegassing process, and then the unit circuit board(s) and the adhesivematerial(s) may be set with stacking one another to obtain a stackedmaterial to be subjected to a second degassing process withoutpressurization.

Such a degassing process(es) makes it possible to obtain an LCP filmhaving extremely low moisture and air contents as the substratematerial, resulting in prevention of local adhesion failure that iscaused by air introduction in a multilayer-laminated body due toinsufficient degassing. In particular, according to the presentinvention, the multilayer circuit board, even having many layers, canavoid insufficient degassing of a film(s) that exist(s) in the centerportion of the multilayer circuit board.

Thermo-Compression Bonding Process

In the thermo-compression bonding process, the circuit board materialsprepared in the preparation process are stacked (overlaid) in accordancewith a predetermined circuit board structure, and the stacked circuitboard materials are thermo-compression bonded by heating at apredetermined pressure.

The circuit board structure to be laminated is not particularly limited,and may have appropriately determined according to the desiredstructure. The circuit board materials are usually stacked so that aconductor layer (or a conductor circuit) is interposed between thecircuit board materials.

It should be noted that the circuit board materials need only to be in astacked structure in the thermo-compression bonding process. The circuitboard materials may be stacked at any time, depending on the state ofthe prepared circuit board materials and work procedures, for example,may be stacked in the process such as preparation process, degassingprocess, and thermo-compression bonding process.

Stacking may be carried out, for example, by sandwiching a bonding sheetbetween at least two sheets of insulating substrates each having aconductor circuit on at least one surface, and optionally by arranging acoverlay on an outermost surface of a stacked body. Alternatively,stacking may be carried out by superposing, without a bonding sheet, atleast two sheets of insulating substrates each having a conductorcircuit on at least one surface, and optionally by placing a coverlay onan outermost surface of a stacked body. Where the insulating substratescan be directly bonded without a bonding sheet, the thickness of theentire circuit board can be reduced.

Thermo-compression bonding of a stacked body can be carried out by usinga vacuum hot press apparatus, a heating roll lamination equipment, orothers, depending on the type of circuit board materials. From theviewpoint of reducing further gas from the LCP film, it is preferable touse a vacuum hot press apparatus. For example, the vacuum hot press maybe preferably carried out by thermo-compression bonding, whilemaintaining the degassed state of the stacked structure achieved byvacuum degassing. The vacuum degree during thermo-compression bondingmay be preferably maintained in the same degree with the vacuum degreeof the second degassing process (e.g., 1500 Pa or below).

Where using a TLCP film that has a thermo-adhesive property enhanced bydegassing process, the heating temperature in the thermo-compressionbonding may be a temperature selected from a broad temperature range,for example, from (Tm−60)° C. to (Tm+40)° C., preferably from (Tm−55)°C. to (Tm+30)° C., and more preferably from (Tm−50)° C. to (Tm+25)° C.,where Tm denotes the melting point of the adhesion-improved TLCP film tobe bonded (in particular, where TLCP films each having different meltingpoint with each other, Tm denotes a lower (lowest) melting point of thefilms). For example, where thermo-compression bonding is carried out ata high temperature environment, the heating temperature may be in arange from (Tm−20)° C. to (Tm+40)° C., (e.g., (Tm−20)° C. to (Tm+20)°C.), preferably about (Tm−10)° C. to (Tm+30)° C., and more preferablyabout (Tm−10)° C. to (Tm+10)° C.

According to the present invention, where the degassing processes (i)and (ii) are combined, surprisingly, it is possible to achieve goodinterlayer adhesion even by heating at a temperature lower than themelting point of the adhesion-improved TLCP film to be adhered. Thethermo-compression bonding may be carried out at a temperature forexample, (Tm−60)° C. or higher and lower than (Tm−20)° C., (Tm−50)° C.or higher and lower than (Tm−30)° C., and more preferably (Tm−40)° C. to(Tm−32)° C.

Also, the pressure applied during thermo-compression bonding can beselected, depending on the LCP film characteristics, for example, from awide range from 0.5 to 6 MPa. According to the present invention, sincean adhesion-improved LCP film(s) undergone the degassing process is(are)used for bonding, good adhesion between LCP film layers can be achievedeven at a pressing pressure of 5 MPa or less, particularly 4.5 MPa orless (for example, 0.5 to 3 MPa, preferably, 1 to 2.5 MPa), resulting inavoidance of local adhesion failure caused by air introduction in acircuit board even after bonding.

According to the present invention, where the degassing process (i) and(ii) are combined, the thermo-compression bonding process may include athermo-compression bonding at a low pressing pressure. For example,thermo-compression bonding process may be carried out under a lowpressure, for example, in a pressing pressure range from 0.5 to 2.5 MPa,preferably 0.6 to 2 MPa, and more preferably 0.7 to 1.5 MPa.

Further, according to the present invention, thermo-compression bondingmay be carried out in a single-stage pressing, or in a multi-stagepressing such as two-stage pressing. For example, a two-stage pressingmay be carried out by pressing under a higher compression pressure (forexample, a range of beyond 2.5 MPa and less than 5 MPa) so as to conducta temporary bonding as a pre-process of the thermo-compression bonding,followed by pressing under the above-described lower compressionpressure. Thermo-compression bonding under the lower compressionpressure may be carried out in a longer time than thermo-compressionbonding time of under the higher compression pressure.Thermo-compression bonding under the low compression pressure may becarried out at a higher temperature than the thermo-compression bondingtemperature under the higher compression pressure.

The time required for the thermo-compression bonding (retention timeunder a constant temperature and pressure) is not particularly limitedas far as the circuit board can have an improved interlayer adhesion,and for example, may be about 15 to 60 minutes, preferably about 20 to50 minutes, and more preferably about 20 to 40 minutes. In the casewhere the multi-stage pressing is carried out, the thermo-compressionbonding time may be the total time of each of the retention times.

It should be noted that the method for producing the circuit board mightinclude, if necessary, various producing processes that are known orconventional (e.g., circuit formation process, through-connectionprocess, inter-layer connection process).

The method for producing a circuit board according to preferable oneembodiment may include:

preparing at least one unit circuit board and at least one TLCP film asa circuit board material to be adhered to the unit circuit board,

-   -   the unit circuit board comprising a thermoplastic liquid crystal        polymer film and a conductor layer formed on one or the both        surfaces of the thermoplastic liquid crystal polymer film, and    -   the circuit board material being adhered to the surface of the        conductor layer;

performing a first degassing of the unit circuit board(s) and thecircuit board material(s) under heating at a temperature ranging from100° C. to 200° C. for a predetermined period of time, for example,under the ambient pressure;

performing a second degassing the of the unit circuit board(s) and thecircuit board material(s) under vacuum of 1500 Pa or lower;

performing integration of a stacked material formed by stacking the atleast one circuit board material and the at least one unit circuit boardby thermo-compression bonding by application of heat and pressure to thestacked material,

wherein the surface of the conductor layer in contact with the circuitboard material has a surface roughness (Rz_(JIS)) of 1.25 μm or less asan average value of ten-points measured according to a method conformingto ISO 4287-1997.

Hereinafter, with reference to the drawings, as an embodiment accordingto the present invention, there may be mentioned a method for producinga circuit board (laminating insulating substrates without a bondingsheet) as well as a method for producing a circuit board (laminatinginsulating substrates with a bonding sheet in between). It should benoted that the scope of the present invention is not limited to theseembodiments.

FIG. 2A is a schematic sectional view showing a circuit board without abonding sheet in a state before insulating substrates are stacked. Hereare prepared a first unit circuit board (double-sided copper-cladlaminate) 10 that comprises a first TLCP film 5 and copper foils 4,4cladded on both surfaces of the film 5; and a second unit circuit board(single-sided copper-clad laminate) 20 that comprises a second TLCP film6 and a copper foil 4 cladded on one surface of the film 6. Here thefirst TLCP film 5 and the second TLCP film 6 may be made of the samematerial, and may have thicknesses being identical or different witheach other.

Then a circuit processing (e.g., a strip line pattern processing) may becarried out to a copper foil to be interposed with the opposed unitcircuit boards so as to obtain a conductor circuit.

Then, preferably in a nitrogen gas atmosphere, the first unit circuitboard 10 and the unit circuit board 20 are heated for a predeterminedtime (first degassing process). The conditions for degassing temperatureand degassing time may follow the conditions described above.

Thereafter, the first unit circuit board 10 and the second unit circuitboard 20 are placed in stack in a chamber of a vacuum hot pressapparatus (not shown) so as to obtain a stacked body 30 as shown in FIG.2B. Then, heating treatment may be carried out for a predetermined time(second degassing process) while retaining a vacuum degree of 1500 Pa orlower by vacuuming. The conditions for degassing temperature anddegassing time may follow the conditions described above.

Then, while maintaining the vacuum degree of 1500 Pa or lower, theheating temperature may be elevated to a temperature for carrying out athermo-compression bonding to laminate each of the layers in the stackedbody 30 under a predetermined compression pressure. The conditions oftemperature as well as period for thermo-compression bonding may followthe conditions described above.

Thereafter, according to a conventional process, the conditions insidethe apparatus are returned to ambient temperature and ambient pressureso as to collect a circuit board 30 from the apparatus.

In the above embodiment, the first unit circuit board 10 is directlyattached to the second unit circuit board 20. Alternatively, as amodified embodiment, if necessary, a bonding sheet may be interposedbetween the first unit circuit board 10 and the second unit circuitboard 20. As a further modified embodiment, a conductive circuit isformed to have a micro-strip line pattern and a coverlay may be usedinstead of the second unit circuit board 20.

Also, in the embodiment shown in FIG. 2B, the circuit board has threeconductor layers. The number of conductor layers may be setappropriately, and may be one or more layers (for example, 2 to 10layers).

FIG. 3A is a schematic sectional view showing a state before laminationof a circuit board where laminating insulating substrates and a bondingsheet. Here are prepared a first unit circuit board (double-sidedcopper-clad laminate) 70 that comprises a first TLCP film 7 and copperfoils 40,40 cladded on both surfaces of the film 7; a second unitcircuit board (single-sided copper-clad laminate) 80 that comprises asecond TLCP film 8 and a copper foil 40 cladded on one surface of thefilm 8; and a bonding sheet 90 of a third TLCP film 9 (a LCP film as anadhesive material) having a melting point lower than both of the TLCPfilms 7 and 8. Here, the first TLCP film 7 and the second TLCP film 8may be made of the same material, and may have thicknesses beingidentical or different with each other.

Then after circuit-processing on the copper foil 40 of each unit circuitboard, the copper foil surface of the first unit circuit board may betreated with FlatBOND GT (produced by MEC Co., Ltd.) to form anoxidation-resistant alloy layer (not shown) on the copper foil surface,and subsequently treated with FlatBOND GC (produced by MEC Co., Ltd.)for applying a silane-coupling agent so as to obtain a conductor layer.

Thereafter, preferably in a nitrogen gas atmosphere, the first unitcircuit board 70, the second unit circuit board 80, and the bondingsheet 90 are heated for a predetermined time (first degassing process).The conditions for degassing temperature and degassing time may followthe conditions described above.

Thereafter, the first unit circuit board 70, the second unit circuitboard 80, and the bonding sheet 90 are placed in stack in a chamber of avacuum hot press apparatus (not shown) so as to obtain a stacked body 50as shown in FIG. 3B. Then, heating treatment may be carried out for apredetermined time (second degassing process) while retaining a vacuumdegree of 1500 Pa or lower by vacuuming. The conditions for degassingtemperature and degassing time may follow the conditions describedabove.

Subsequently, while maintaining the vacuum degree of 1500 Pa or lower,the heating temperature is elevated to a temperature condition forcarrying out a thermo-compression bonding to laminate the layers witheach other in the stacked body 50 under a predetermined compressionpressure. The conditions of temperature as well as period forthermo-compression bonding may follow the conditions described above.

Thereafter, according to a conventional process, the conditions insidethe apparatus are returned to ambient temperature and ambient pressureso as to collect a circuit board 50 from the apparatus.

In the embodiments described above, the second unit circuit board islaminated to the first unit circuit board with or without a bondingsheet. The first unit circuit board comprises an insulating layer andconductor layers (copper foils) placed on both surfaces of theinsulating layer. The second unit circuit board comprises an insulatinglayer and a conductor layer on one surface (upper surface) of theinsulating layer. However, the configuration illustrated is not intendedto limit the circuit board of the present invention. For example, thecircuit board may have two conductor layers, or four or more conductorlayers. The circuit board may comprise a coverlay of a LCP film to coverthe conductor layer on the outermost layer.

Circuit Board

The circuit board (preferably a multi-layer circuit board) according tothe fourth aspect of the present invention relates to a circuit boardcomprising a plurality of circuit board materials, wherein:

the circuit board materials are at least one member selected from thegroup consisting of an insulating substrate having a conductor layer onat least one surface, a bonding sheet, and a coverlay; and

at least one of the circuit board materials comprises a TLCP film.

The circuit board has an improved heat resistance, and is a circuitboard showing a solder heat resistance when the circuit board is placedin a solder bath at a temperature of 290° C. for 60 seconds conformingto a method of JIS C 5012. The solder heat resistance may be evaluatedby observing a substrate sample that is subjected to solder float testin a solder bath at a temperature of 290° C. for 60 seconds conformingto a method of JIS C 5012 to be determined whether the substrate samplehas blisters having a height of 100 μm or higher by sight or using anoptical microscopy (5 magnifications or higher).

For example, the circuit board of the present invention may be a circuitboard having the following configuration:

(i) a circuit board (multilayer or laminated circuit board) thatcomprises two or more unit circuit boards each including an insulatinglayer of a TLCP film (a first TLCP film) and a conductor layer(s) formedon one or both surfaces of the film, and a bonding sheet(s) interposingbetween the unit circuit boards,

(ii) a circuit board (single layer or bilayer circuit board) thatcomprises a unit circuit board including an insulating layer of a TLCPfilm (a first LCP film) and a conductor layer(s) formed on one or bothsurfaces of the film, and a coverlay(s) to cover the conductor layer(s)of the unit circuit board,

(iii) a configuration combining the above (i) and (ii), for example, acircuit board (multilayer or laminated circuit board) that comprises aunit circuit board, a bonding sheet(s), and a coverlay(s) to cover theconductor layer(s) of the unit circuit board, wherein the bondingsheet(s) interposes between the unit circuit board, and the outermostlayer of the circuit board comprises the coverlay covering the conductorlayer(s) of the unit circuit board,

(iv) a circuit board (multilayer or laminated circuit board) thatcomprises two or more unit circuit boards, each including an insulatinglayer of a TLCP film (a substrate layer), wherein the unit circuitboards are directly laminated without a bonding sheet(s), and

(v) a configuration combining the above (ii) and (iv), for example, acircuit board (multilayer or laminated circuit board) that comprises twoor more unit circuit boards and a coverlay(s), wherein the unit circuitboards are directly laminated without a bonding sheet, and the outermostlayer of the circuit board comprises the coverlay covering the conductorlayer(s) of the unit circuit board.

It should be noted that, as already mentioned in the producing method, asurface of the conductor layer on the side of bonding to a circuit boardmaterial may have a surface roughness (Rz_(JIS)) of 1.25 μm or less asan average value of ten-points measured according to a method conformingto ISO4287-1997.

Further, since the adhesive property of the TLCP film is improved in theabove circuit board, the circuit board may have an improved bondingstrength between the TLCP film and a circuit board material in contactwith the TLCP film, as a value measured in accordance with JISC5016-1994. Where the circuit board material is an insulating substratematerial (preferably, another TLCP film), the bonding strength betweenthe TLCP film and the insulating substrate material may be 0.8 kN/m orhigher (e.g., 0.8 to 3 kN/m), preferably 0.9 kN/m or higher, morepreferably 1 kN/m or higher, and further preferably 1.1 kN/m or higher.It should be noted that the bonding strength may be determined as a peelstrength value measured conforming to JIS C5016-1994 by peeling a TLCPfilm from an adherend at a peeling angle of 90° and at a peeling rate of50 mm per minute using a tensile tester (“Digital force gauge FGP-2”produced by NIDEC-SHIMPO CORPORATION.).

Further, since the adhesive property of the LCP film is improved in theabove circuit board, where the circuit board material is a conductorlayer, the bonding strength in accordance with JIS C5016-1994 betweenthe TLCP film and the conductor layer may be 0.3 kN/m or higher (e.g.,0.3 to 2 kN/m), and preferably 0.5 kN/m or higher.

It should be noted that upon determining interlayer adhesion, existenceof cohesive failure could be generally determined as an evidence of goodbonding. In contrast, occurrence of interfacial separation shows poorbonding in many cases.

Preferably, the circuit board is generally improved in bonding strengthin every direction. For example, with respect to a first direction (Adirection) of a circuit board sample and a second direction (Bdirection) perpendicular to the first direction, where bonding strengthsof the sample are measured in four direction by peeling from both sides,i.e., in a forward A direction, in an adverse A direction, in a forwardB direction, and in an adverse B direction,

(i) the minimum bonding strength in the four directions between the TLCPfilm and an insulating substrate material may be 0.5 kN/m or higher(e.g., 0.5 to 3 kN/m), preferably 0.6 kN/m or higher, more preferably0.7 kN/m or higher, still more preferably 0.8 kN/m or higher, andparticularly preferably 0.9 kN/m or higher, and/or

(ii) the minimum bonding strength in the four directions between theTLCP film and a conductor layer may be 0.25 kN/m or higher (e.g., 0.25to 2 kN/m), preferably 0.28 kN/m or higher, and more preferably 0.5 kN/mor higher.

In the circuit board comprising the circuit board materials, the circuitboard materials may comprise at least two TLCP films including a firstTLCP film and a second TLCP film, wherein a conductor layer isinterposed between the first and the second TLCP films. The differencein melting point between the first TLCP film and the second TLCP filmmay be in the range described above. Also, in order to enhance highfrequency characteristics, all of the circuit board materials preferablycomprise TLCP films.

Moreover, depending on thermo-adhesive property of TLCP films, thecircuit board may have a configuration without a bonding sheet, i.e.,direct bonding of insulating substrates with each other, or directbonding of an insulating substrate and a coverlay. For example, non-useof the bonding sheet makes it possible to achieve a circuit board with areduced thickness.

For example, as shown in FIG. 4, the circuit board may comprise n layersof conductor layer 4 and n+1 layers of insulating layer (or a TLCP filmlayer) 3 wherein each of the conductor layers is interposed between theinsulating layers. In this case, if necessary, the circuit board may beprovided with a conductor layer on the outermost layer. It should benoted that where one portion of the conductor layer is originally formedon an upper layer of an insulating layer and another portion of theconductor layer is originally formed on a lower layer of an insulatinglayer, as long as these parts are interposed between the same insulatinglayers, these parts are regarded as belonging to the same conductorlayer.

Further, since the circuit board with an adhesive-improved TLCP film(s)makes it possible to be thermo-compression bonded at a lower pressure(preferably, at a lower temperature and lower pressure). As a result,the subduction (sinking) of the conductor circuit, the subduction beingcaused in the thermo-compression bonding, can be reduced, resulting inimprovement in reliability of the circuit board.

For example, FIG. 5A shows a schematic cross-sectional view showing alaminate sample comprising a conductor circuit 4, and LCP films 5 and 6obtained by cutting the sample vertically to the conductor circuit.Where L1 denotes the thickness of the LCP film 5 at which the conductorcircuit 4 is not formed, and L2 denotes the thickness of the insulatingsubstrate at which the conductor circuit is formed, the measuredthicknesses L1 and L2 can be used for calculating a L2/L1 ratio inpercentage that an index parameter for subduction. The ratio of L2/L1 inpercentage may be 80 to 100%, preferably 85 to 100%, and more preferably90 to 100%. It should be noted that where there is no subduction, theratio is 100% because of L1=L2. The larger the subduction amount is, thelower the percent ratio is. The thickness L2 may be measured as adistance L2 between the lower surface of the conductor circuit 4 and thebottom surface of the LCP film 5.

As shown in FIG. 5B, where a ground conductor 4 b is formed on thebottom surface of the LCP film, the L1 may be determined as a distancefrom the boundary surface between the adjacent LCP films to the uppersurface of the ground conductor 4 b. The L2 may be determined as adistance from the lower surface of the conductor circuit 4 a to theupper surface of the ground conductor 4 b in the circuit board.

Since the circuit board according to the present invention can employ,as an insulating material, a thermoplastic liquid crystal polymerexcellent in dielectric characteristics, the circuit board can be usedparticularly suitably as a high frequency circuit board. Examples ofhigh frequency circuits include a circuit for transmitting mainly (only)high frequency signals; in addition; a circuit for a transmission linetransmitting low frequency signals, for example, a circuit for atransmission line transmitting low frequency signals as output afterconverting high frequency signals into low frequency signals, a circuitfor a transmission line supplying electronic power to drive highfrequency-corresponding parts; as well as a circuit provided with theabove circuits or transmission lines on the same plane.

For example, at a frequency of 10 GHz, the circuit board (ε_(r)) mayhave a relative dielectric constant of, for example, from 2.6 to 3.5,and more preferably from 2.6 to 3.4.

Also, for example, at a frequency of 10 GHz, the circuit board may havea dielectric loss tangent (Tan δ) of, for example, from 0.001 to 0.01,and more preferably from 0.001 to 0.008.

EXAMPLES

Hereinafter, the present invention is described in greater detail byexamples, but the invention is not limited in any way by the presentinvention to this embodiment. In the following Examples and ComparativeExamples were measured for various physical properties by the followingmethod.

Melting Point

Melting point of a film was determined based on the observation ofthermal behavior of the film using a differential scanning calorimeter.A test film was heated at a rate of 20° C./min to completely melt thefilm, and the melt was rapidly cooled to 50° C. at a rate of 50° C./min.Subsequently, the quenched material was reheated at a heating rate of20° C./minute, and a position of an endothermic peak appearing in thereheating process was recorded as a melting point of the film.

Moisture Content

Karl Fischer method was employed as a measuring method of moisturecontent, that is, moisture content was measured by observing change inpotential difference before and after allowing moisture absorbed in asolvent in accordance with the principle of the Karl Fischer titration.

(1) Device name for trace moisture measurement: VA-07, CA-07 availablefrom Mitsubishi Chemical Analytech Co., Ltd.

(2) Heating temperature: 260° C.

(3) N₂ purge pressure: 150 mL/min.

(4) Measurement preparation (automatic)

-   -   Purge: 1 minute    -   Pre-heat: 2 minutes for baking a sample board    -   Cooling: 2 minutes for cooling the sample board

(5) Measurement

-   -   Time for accumulating moisture in a measurement titration cell,        i.e., time for sending moisture with N₂: 3 minutes

(6) Sample weight: 1.0 to 1.3 g

Segment Orientation Ratio (SOR)

Using a microwave type molecular orientation meter, a liquid crystalpolymer film is inserted into a microwave resonance waveguide tube suchthat a propagation direction of microwave is perpendicular to the filmsurface, and electric-field strength (microwave transmission intensity)of microwave transmitting through the film is measured. Then, based onthe measured value, m value (referred to as refractive index) iscalculated from the following formula:

m=(Zo/Δz)×[1−νmax/νo]

Here, Zo represents a device constant, Δz represents an averagethickness of an object subjected to the measurement, νmax represents thefrequency at which the maximum microwave transmission intensity can beobtained when the frequency of the microwave is varied, and νorepresents the frequency at which the maximum microwave transmissionintensity can be obtained when the average thickness is zero, that is,when no object is present.

Next, when the rotation angle of the object relative to the direction ofoscillation of the microwaves is 0°, that is, when the direction ofoscillation of the microwaves is aligned with the direction in whichmolecules of the object are most oriented as well as in which theminimum microwave transmission intensity is exhibited, an m valueobtained in such a case was represented as m₀. An m value obtained as mrepresents the value of the refractive index when the angle of rotationof the object is 90°. A segment orientation ratio SOR was calculated asm₀/m₉₀.

Film Thickness

Thicknesses of an obtained film were measured at intervals of 1 cm inthe TD direction using a digital thickness meter (manufactured byMitutoyo Corporation), and the film thickness was determined as anaverage thicknesses of 10 points arbitrarily selected from a centerportion and end portions.

Heat Resistance Test

Solder float test was carried in conformity with JIS C 5012 to examinesolder heat resistance of the circuit board. The solder heat resistancewas evaluated by observing a substrate sample that was subjected tosolder float test in a solder bath of 290° C. for 60 seconds whether thesubstrate sample had at least one blister having an area of 100 μm×100μm or wider by sight or using an optical microscopy (5 magnifications orhigher).

Specifically, from a circuit board sample having a size of 30 cm square(30 cm×30 cm) were derived five circuit board samples each having a sizeof 5 cm square (5 cm×5 cm) by randomly cutting. Each of the five circuitboard samples were subjected to the solder float test, and blisteroccurrence was observed by sight or using an optical microscopy (5magnifications or higher). Where blister was not observed in all of thefive cut samples, the originated circuit board sample was determined asgood, i.e., showing solder heat resistance. Where blister was observedin any one of the five cut samples, the originated circuit board samplewas determined as poor.

Method for Measuring Bonding Strength between Adjacent Circuit BoardMaterials

In conformity to JIS C5016-1994, peel strength was measured by peelingone of two bonding circuit board materials from the other material at apeeling angle of 90° and at a peeling rate of 50 mm per minute using atensile tester [“Digital force gauge FGP-2” produced by NIDEC-SHIMPOCORPORATION.]. The obtained value was regarded as bonding strength(peeling strength).

It should be noted that bonding strength was measured in four directionswith respect to a first direction (MD direction) of a circuit boardsample and a second direction (TD direction) perpendicular to the firstdirection, by peeling from both sides, i.e., in a forward MD direction(or MD-proceeding direction), in an adverse MD direction (orMD-reversing direction), in a forward TD direction (or rightward TDdirection), and in an adverse TD direction (or leftward TD direction).The average value in the four directions was treated as a representativebonding strength of the circuit board.

It should be noted that where circuit board material has a conductivematerial, bonding strength is determined depending on the surface arearatio of the conductive material portion in contact with the TLCP film.The surface area ratio may be determined as existing ratio of conductivematerial as follows:

$\begin{matrix}{{Existin}\; g\mspace{11mu} {ratio}} \\{{of}\mspace{14mu} {conductive}\mspace{14mu} {material}}\end{matrix} = {{\begin{pmatrix}{{Surface}\mspace{14mu} {area}\mspace{14mu} {of}\mspace{14mu} {circuit}\mspace{20mu} {patterns}\mspace{14mu} {on}} \\{{circuit}\mspace{14mu} {board}\mspace{14mu} {unit}\mspace{14mu} {in}\mspace{14mu} {contact}\mspace{14mu} {with}\mspace{14mu} {the}\mspace{14mu} {target}\mspace{14mu} {LCP}\mspace{14mu} {film}}\end{pmatrix}/\begin{pmatrix}{{Surface}\mspace{14mu} {area}\mspace{14mu} {of}\mspace{14mu} {entire}} \\{{circuit}\mspace{14mu} {board}\mspace{14mu} {unit}}\end{pmatrix}} \times 100}$

Where the ratio is 30% or more, the bonding strength was measured as abonding strength between the LCP film and a conductor layer. Where theratio is less than 30%, the bonding strength was measured as a bondingstrength between the LCP film and an insulating substrate material.

Method for Measuring Surface Roughness

A copper foil surface in a laminate (B) was subjected to rougheningtreatment, and then an arithmetic mean roughness (Ra) and a surfaceroughness (Rz_(JIS)) of the treated surface were measured using astylus-type surface roughness tester (“SJ-201” produced by MitutoyoCorp.). Measurement was carried out conforming to ISO 4287-1997. Morespecifically, the arithmetic mean roughness Ra is a value that shows anaverage value of the absolute value of the deviation from the mean line;the surface roughness (Rz_(JIS)) is an average value of ten pointsselected from a roughness curve in a sampled standard length along thedirection of the average line as the sum of the average of the absolutevalues of the 5 highest peak points (convex top points) and the averageof the absolute values of the 5 lowest valley points (concave bottompoints) in the sampled section, and is express in μm.

Subduction

A laminate containing a conductor circuit was cut to give across-sectional sample vertical to the conductor circuit. The sample wasplaced on a Pt sputtering machine to form a Pt film (thickness: 20 Å) onthe surface. Then, using a scanning electron microscope (“SU-70”produced by Hitachi High-Technologies Corporation.), secondary electronimage of the laminate in the cross section (SEM image) was obtained atan accelerating voltage of 5 kV to observe the degree of subduction.

As shown in FIG. 5B, with respect to a laminate containing LCP films anda ground conductor adjacent to one of the LCP film, the L1 wasdetermined as a distance from the boundary surface between the adjacentLCP films to the ground conductor; the L2 was determined as a distancefrom the lower surface of the conductor circuit to the upper surface ofthe ground conductor in the circuit board. After calculating a ratio ofL2/L1 in percentage, subduction of the circuit board was evaluated inaccordance with the following criteria:

Good: Ratio of L2/L1 is 80% or more.

Poor: Ratio of L2/L1 is less than 80%.

Where no subduction occurred, the ratio is 100% because of L1=L2. Thelarger subduction is, the lower the percentage ratio is.

Resin Flow

Occurrence of resin flow in 10 cm circuit board samples was visuallyobserved. A sample having a resin flow of 1 mm or less was determined asgood in quality; a sample having a resin flow of over 1 mm wasdetermined as poor in quality.

Example 1

(1) Production of Adhesive-Improved LCP Film

A copolymerization product of p-hydroxybenzoic acid and6-hydroxy-2-naphthoic acid (mole ratio: 73/27), being a thermoplasticliquid crystal polymer having a melting point of 280° C., was melted andextruded by inflation method to obtain a rolled product (windingthickness W=600 mm) of a thermoplastic liquid crystal polymer filmhaving a melting point of 280° C., a film thickness of 50 μm, and asegment orientation ratio SOR of 1.02. The TLCP film in the rolledproduct had a moisture content of 400 ppm.

Thus obtained TLCP film rolled product was degassed by heat treatmentfor 60 minutes at a temperature of 120° C. Thus-degassed TLCP film inthe rolled product had a moisture content of 200 ppm and a segmentorientation ratio SOR of 1.02.

(2) Production of Unit Circuit Board

From a copolymerization product of p-hydroxybenzoic acid and6-hydroxy-2-naphthoic acid (mole ratio: 73/27) was obtained a TLCP filmhaving a melting point of 280° C. and a film thickness of 50 μm. TheTLCP film was heat-treated under nitrogen atmosphere at 260° C. for 4hours, and at 280° C. for another 2 hours to increase a melting pointinto 325° C. Onto each surface of the film, a rolled copper foil (JXNippon Mining & Metals Corporation, BHYX-T-12, thickness: 12 μm) was setto be laminated using a continuous heat-pressing machine with a pair ofrolls at a roll temperature of 290° C., a linear pressure of 100 kg/cm,a line speed of 2 m/min to obtain a copper-clad laminate. Thecopper-clad laminate was processed to produce a unit circuit boardhaving a strip line structure. The TLCP film in the unit circuit boardhad a moisture content of 400 ppm.

(3) Production of Multilayer Circuit Board

The adhesive-improved LCP film obtained in the process (1) was used as abonding sheet to be interposed between two sheets of the unit circuitboards to obtain a stacked material. The stacked material was placed ina vacuum heat press apparatus. Thereafter, the stacked material wasthermo-compression bonded under vacuum at a vacuum degree of 1300 Pa anda compression pressure of 4 MPa at 300° C. for 30 minutes to be bondedwith each other to obtain a circuit board having a configuration of unitcircuit board/bonding sheet/unit circuit board. The obtained circuitboard was evaluated in various physical properties. Table 7 showsobtained properties.

Example 2

(1) Production of Circuit Board

A stacked material was prepared in the same manner with Example 1 exceptfor using, as a bonding sheet, a non-degassed TLCP film having a meltingpoint of 280° C., a film thickness of 50 μm, a moisture content of 400ppm, and a segment orientation ratio SOR of 1.02 obtained from acopolymerization product of p-hydroxybenzoic acid and6-hydroxy-2-naphthoic acid (mole ratio: 73/27). The stacked material inwhich the bonding sheet was interposed between two sheets of the unitcircuit boards was placed in a vacuum heat press apparatus.

Thereafter, the stacked material was subjected to degassing under vacuumat a vacuum degree of 1000 Pa and a compression pressure of 0.5 MPa at120° C. for 60 minutes to be degassed in the stacked configuration.

After degassing under vacuum, the stacked material was subjected tothermo-compression bonding in the same way as Example 1 to be bondedwith each other to obtain a circuit board having a configuration of unitcircuit board/bonding sheet/unit circuit board. The obtained circuitboard was evaluated in various physical properties. Table 7 showsobtained properties.

Example 3

(1) Production of Circuit Board

A circuit board was prepared in the same manner with Example 2 exceptfor using, as a bonding sheet, an adhesive-improved TLCP film obtainedin Example 1. The obtained circuit board was evaluated in variousphysical properties. Table 7 shows obtained properties.

Comparative Example 1

(1) Production of Circuit Board

A circuit board was prepared in the same manner with Example 1 exceptfor using, as a bonding sheet, a non-degassed TLCP film having a meltingpoint of 280° C., a film thickness of 50 μm, a moisture content of 400ppm, and a segment orientation ratio SOR of 1.02 obtained from acopolymerization product of p-hydroxybenzoic acid and6-hydroxy-2-naphthoic acid (mole ratio: 73/27). The obtained circuitboard was evaluated in various physical properties. Table 7 showsobtained properties.

TABLE 7 Circuit board unit Bonding sheet Degass under vacuum MoistureMoisture Vacuum Insulating content content degree Temp. Pressure Periodsubstrate (ppm) Film (ppm) SOR (Pa) (° C.) (MPa) (min) Ex. 1 LCP film400 Adhesive-improved 200 1.02 — — — — (Tm325° C.) LCP film (Tm280° C.)Ex. 2 LCP film 400 LCP film 400 1.02 1000 120 0.5 60 (Tm325° C.) (Tm280°C.) Ex. 3 LCP film 400 Adhesive-improved 200 1.02 1000 120 0.5 60(Tm325° C.) LCP film Com. Ex. 1 LCP film 400 LCP film 400 1.02 — — — —(Tm325° C.) (Tm280° C.) Thermo-compression bonding Circuit board VacuumHeat Bonding degree Temp. Pressure Period resistance strength (Pa) (°C.) (MPa) (min) (290° C.) (kN/m) Ex. 1 1300 300 4 30 Good 1.0 Ex. 2 1300300 4 30 Good 1.0 Ex. 3 1300 300 4 30 Good 1.5 Com. Ex. 1 1300 300 4 30Poor 0.5

As shown in Table 7, since each of the circuit boards in Examples 1 and3 uses the adhesive-improved LCP film as a bonding sheet, the interlayeradhesion of the circuit boards can be improved even in the conventionalthermo-compression bonding procedure. These circuit boards also haveenhanced heat resistance so that occurrence of blisters can besuppressed at high temperatures.

Meanwhile, Example 2 does not employ the adhesive-improved LCP film asthe circuit board material. However, because of the degassing processfor the stacked material under vacuum before thermo-compression bonding,the interlayer adhesion of the circuit board can be also enhanced afterthermo-compression bonding. The circuit board also has enhanced heatresistance so that occurrence of blisters can be suppressed at hightemperatures.

In particular, in Example 3, usage of the adhesion-improved LCP film asthe bonding sheet in combination with the specific degassing processmakes it possible to achieve particularly excellent interlayer adhesion.

On the other hand, Comparative Example 1, which neither employs theadhesion-improved LCP film nor is subjected to the degassing process,deteriorates in interlayer adhesion, showing lower bonding strength thanthose in Examples. Further, some samples in Comparative Example 1 haveblisters at the high temperature.

Example 4

(1) Production of Unit Circuit Board

Onto each surface of a TLCP film having a melting point of 335° C.(“CT-Z”, produced by Kuraray Co., Ltd., thickness: 25 μm), a rolledcopper foil (“BHYX-T-12”, produced by X Nippon Mining & MetalsCorporation, thickness: 12 μm) was overlaid to obtain a stackedmaterial. The stacked material was placed in a vacuum heat pressapparatus with heated plates at 295° C. under a compression pressure of4 MPa for 10 minutes to be bonded with each other to obtain a firstcopper-clad laminate having a configuration of copper foil/first TLCPfilm/copper foil. In the meantime, onto each surface of a TLCP filmhaving a melting point of 280° C. (“CT-F”, produced by Kuraray Co.,Ltd., thickness: 50 μm), a rolled copper foil (“BHYX-T-12”, produced byJ Nippon Mining & Metals Corporation, thickness: 12 μm) was overlaid toobtain a stacked material. The stacked material was placed in a vacuumheat press apparatus with heated plates at 275° C. under a compressionpressure of 4 MPa for 10 minutes to be bonded with each other to obtaina second copper-clad laminate having a configuration of copperfoil/second TLCP film.

Subsequently, one copper foil of the first copper-clad laminate wasprocessed by a chemical etching process to have a circuit pattern of astrip line structure (existing conductive material ratio: less than 30%)to obtain a first unit circuit board.

The first unit circuit board and the second copper-clad laminate werestacked so that the circuit pattern was interposed between the first andsecond TLCP films to obtain a stacked material. The stacked material wassubjected to degassing under heating at 100° C. under atmosphericpressure at a pressing pressure of 0 MPa for 1 hour (a first degassingprocess: degassing under heating).

Subsequently, the stacked material of the first unit circuit board andthe second copper-clad laminate, in which the circuit pattern wasinterposed between the first and second TLCP films, was placed in achamber of a vacuum hot press apparatus for degassing under vacuum at avacuum degree of 1000 Pa with heating at 100° C. under a compressionpressure of 0 MPa for 1 hour (second degassing: degassing under vacuum).

Then, the stacked material was subjected to two-stage press, i.e., firstcompression-bonding by means of heated plates set to 150° C. under acompression pressure of 4 MPa for 5 minutes (pre-process), followed bysecond compression-bonding by means of heated plates set to 300° C.under a compression pressure of 1 MPa for 30 minutes (post-process) toobtain a circuit board having a multilayer configuration of copperfoil/first TLCP layer/circuit layer/second TLCP layer/copper foil. Theobtained circuit board was evaluated in various physical properties.Table 8 shows obtained properties.

It should be noted that FIG. 6A shows an SEM image of thus-obtainedcircuit board. As shown in FIG. 6A, in which the white portion showsliquid crystal polymer, the boundary surface between the first TLCPlayer and the second TLCP layer can be observed. A copper stripe or thecopper foil portion can be observed as a white or high contrast part inmonochrome. Observation of FIG. 6A reveals that subduction of circuitlayer into the TLCP layer is suppressed.

Example 5

Onto each surface of a TLCP film having a melting point of 335° C.(“CT-Z”, produced by Kuraray Co., Ltd., thickness: 25 μm), a rolledcopper foil (“BHYX-T-12”, produced by JX Nippon Mining & MetalsCorporation, thickness: 12 μm) was overlaid to obtain a stackedmaterial. The stacked material was placed in a vacuum heat pressapparatus with heated plates at 295° C. under a compression pressure of4 MPa for 10 minutes to be bonded with each other to obtain a secondcopper-clad laminate having a configuration of copper foil/second TLCPfilm. The circuit board was produced in the same manner with Example 4except for using the second copper-clad laminate as obtained above. Theobtained circuit board was evaluated in various physical properties.Table 8 shows obtained properties.

It should be noted that FIG. 6B shows an SEM image of thus-obtainedcircuit board. Observation of FIG. 6B reveals that subduction of circuitlayer into the TLCP layer is suppressed.

Comparative Example 2

A circuit board was produced in the same manner as in Example 4 exceptfor carrying out neither degassing under heating nor degassing undervacuum. The obtained circuit board was evaluated in various physicalproperties. Table 8 shows obtained properties.

Comparative Example 3

A circuit board was produced in the same manner as in Example 5 exceptfor carrying out neither degassing under heating nor degassing undervacuum. The obtained circuit board was evaluated in various physicalproperties. Table 8 shows obtained properties.

Comparative Example 4

A circuit board was produced in the same manner as in Example 5 exceptthat neither degassing under heating nor degassing under vacuum wascarried out, and that two-stage press was carried out in thethermo-compression bonding, i.e., in a first compression-bonding bymeans of heated plates set to 150° C. under a compression pressure of 4MPa for 5 minutes (pre-process), followed by second compression-bondingby means of heated plates set to 320° C. under a compression pressure of3 MPa for 30 minutes (post-process). The obtained circuit board wasevaluated in various physical properties. Table 8 shows obtainedproperties.

It should be noted that FIG. 6C shows an SEM image of thus-obtainedcircuit board. Observation of FIG. 6C reveals that the circuit layer issubducted into the LCP layer.

TABLE 8 Second Circuit board material degassing Second First degassingVacuum First LCP LCP Environ- Temp. Pressure Period degree Temp.Pressure Period film film ment (° C.) (MPa) (min) (Pa) (° C.) (MPa)(min) Ex. 4 CTZ-25 CTF-50 Ambient 100 0 60 1000 100 0 60 (Tm335° C.)(Tm280° C.) pressure Ex. 5 CTZ-25 CTZ-50 Ambient 100 0 60 1000 100 0 60(Tm335° C.) (Tm335° C.) pressure Com. Ex. 2 CTZ-25 CTF-50 — — — — — — —— (Tm335° C.) (Tm280° C.) Com. Ex. 3 CTZ-25 CTZ-50 — — — — — — — —(Tm335° C.) (Tm335° C.) Com. Ex. 4 CTZ-25 CTZ-50 — — — — — — — — (Tm335°C.) (Tm335° C.) Thermo- Bonding strength compression LCP film/LCP HeatCompression Pressure film (kN/m) resistance Resin Temp (° C.) (MPa) Max.Min. Avg. (290° C.) flow Subduction Ex. 4 300 1.0 1.80 1.50 1.70 GoodGood Good Ex. 5 300 1.0 1.20 1.00 1.05 Good Good Good Com. Ex. 2 300 1.00.80 0.60 0.63 Poor Good Good Com. Ex. 3 300 1.0 0.80 0.60 0.63 PoorGood Good Com. Ex. 4 320 3.0 1.30 1.10 1.14 Poor Poor Poor

As shown in Table 8, since each of the circuit boards in Examples 4 and5 uses the LCP film subjected to the specific degassing process, theheat resistance of the circuit boards is improved. Further, even if thepost-process as the main thermo-compression bonding is carried out undera low compression pressure of 1 MPa, it is possible to improveinterlayer adhesion in the circuit board (between the adjacent TLCPfilms as well as between the TLCP film and the conductive layer). Inparticular, Examples 4 and 5 achieve satisfactory adhesion of directlybonding between unit circuit boards even without a bonding sheet used inExamples 1 to 3.

In addition, the production of these circuit boards under lowcompression pressure of 1 MPa in the main thermo-compression bondingprocess makes it possible to suppress not only resin flow during circuitboard production but also subduction of the conductor layer into theTLCP film.

Furthermore, in Example 5, even if both of the TLCP films arehigh-melting-point films, it is possible to achieve satisfactoryadhesion between the circuit board materials. Particularly surprisingly,in Example 5, even if the thermo-compression bonding is carried out at atemperature lower than the melting point of these high melting pointfilms, it is possible to show satisfactory interlayer adhesion.

On the other hand, in Comparative Example 2 and Comparative Example 3,because of lack in degassing process, the obtained circuit boards areinferior in heat resistance as well as in interlayer adhesion beingreduced by about 40% compared with the interlayer adhesion of Example 5.

In Comparative Example 4, since the production of the circuit board wascarried out at a high temperature under high compression pressure in themain thermo-compression bonding process, bonding strength is improvedwhereas heat resistance is deteriorated. Further, resin flow is occurredduring circuit board production, and the conductor layer is subductedinto the TLCP film.

Various properties measured in the above Examples show advantageousproperties such as heat resistance and interlayer adhesion in thecombination of the insulating substrate and the bonding film, thecombination of the insulating substrate and the coverlay, and thecombination of the insulating substrate and the insulating substrate.

Next, on the basis of Examples 6 to 8 and Comparative Example 5, theinfluence of the surface roughness of the conductor layer on the circuitboard will be discussed.

Example 6

Onto each surface of a TLCP film having a melting point of 335° C.(“CT-Z”, produced by Kuraray Co., Ltd.), a rolled copper foil(“BHYX-T-12”, produced by JX Nippon Mining & Metals Corporation,thickness: 12 μm) was overlaid to obtain a stacked material. The stackedmaterial was placed in a vacuum heat press apparatus with heated platesat 295° C. under a compression pressure of 4 MPa for 10 minutes to bebonded with each other to obtain a first unit circuit board having aconfiguration of copper foil/TLCP film/copper foil as well as a secondunit circuit board having a configuration of copper foil/TLCP film. Thethicknesses of the TLCP films in the first unit circuit board and thesecond unit circuit board are 100 μm and 75 μm, respectively.Subsequently, each of the copper foils was processed by a chemicaletching method (existing conductive material ratio: 30% or more).

Subsequently, the copper foils of the first unit circuit board weretreated by a surface roughening treatment, more specifically, atreatment carried out with “FlatBOND GT and FlatBOND GC treatment”available from MEC Co., Ltd. Hereinafter this treatment is referred toas FlatBOND treatment. The conductor layer including an alloy layer hadsurface roughness Ra of 0.13 μm and Rz_(JIS) of 1.05 μm.

The first unit circuit board, a bonding sheet (a TLCP film “CT-F” havinga melting point of 280° C. and a thickness of 25 μm produced by KurarayCo., Ltd.) and the second unit circuit board were overlaid in this orderto obtain a stacked material. The stacked material was subjected todegassing under heating at 115° C. under atmospheric pressure, at acompression pressure of 0 MPa for 2 hours (a first degassing process).

Subsequently, as shown in FIG. 3B, the stacked material of the firstunit circuit board and the second copper-clad laminate, in which thebonding sheet was interposed between the first and second unit circuitboards, was placed in a chamber of a vacuum hot press apparatus fordegassing under vacuum at a vacuum degree of 1000 Pa with heating at 00°C. under a compression pressure of 0 MPa for 1 hour (second degassing).

Then, the stacked material was subjected to thermo-compression bondingby means of heated plates set to 295° C. under a compression pressure of1 MPa for 30 minutes (pre-process) to obtain a circuit board having amultilayer configuration of copper foil/first TLCP layer/second TLCPlayer/circuit layer/first TLCP layer/copper foil as shown in FIG. 3B.

The obtained circuit board was evaluated in heat resistance, bondingstrength, flowing property, and subduction of circuit layer. Table 9shows obtained properties.

Example 7

A circuit board was produced in the same manner as in Example 6 exceptthat the FlatBOND treatment was not carried out to the copper foils inthe first unit circuit board. The obtained circuit board was evaluatedin heat resistance, bonding strength, flowing property, and subductionof circuit layer. Table 9 shows obtained properties. It should be notedthat the copper foil constituting the conductor layer had surfaceroughness Ra of 0.14 m and Rz_(JIS) of 1.09 μm.

Example 8

A circuit board was produced in the same manner as in Example 6 exceptthat the surface roughening was carried out by a blackening treatment,which belongs to a conventional surface roughening treatment, instead ofthe FlatBOND treatment, and that the compression pressure was changedinto 4 MPa. The obtained circuit board was evaluated in heat resistance,bonding strength, flowing property, and subduction of circuit layer.Table 9 shows obtained properties.

It should be noted that the blackening treatment was carried out byimmersing the first unit circuit board for 2 minutes into a blackeningtreatment solution (aqueous solution) containing 31 g/L of sodiumsulfite, 15 g/L of sodium hydroxide, 12 g/L of sodium phosphate kept ina warm bath at 95° C., followed by washing the immersed first unitcircuit board with water and drying. The copper foil constituting theconductor layer had surface roughness Ra of 0.18 μm and Rz_(JIS) of 1.31μm.

Comparative Example 5

A circuit board was produced in the same manner as in Example 8 exceptfor carrying out neither degassing under heating nor degassing undervacuum. The obtained circuit board was evaluated in various physicalproperties. Table 9 shows obtained properties.

TABLE 9 Circuit board unit Second degassing Conductor layer Firstdegassing Vacuum Insulating roughness (μm) Bonding Environ- Temp.Pressure Period degree Temp. Pressure Period substrate Ra

sheet ment (° C.) (MPa) (min) (Pa) (° C.) (MPa) (min) Ex. 6 LCP film0.13 1.05 LCP film Ambient 115 0 120 1000 100 0 60 (Tm335° C.) (Tm280°C.) pressure Ex. 7 LCP film 0.14 1.09 LCP film Ambient 115 0 120 2000100 0 60 (Tm335° C.) (Tm280° C.) pressure Ex. 8 LCP film 0.18 1.31 LCPfilm Ambient 115 0 120 1000 100 0 60 (Tm335° C.) (Tm280° C.) pressureCom. LCP film 0.18 1.31 CCP film — — — — — — — — Ex. 5 (Tm335° C.)(Tm280° C.) Thermo-compression Bonding Strength LCP Vacuumfilm/Conductor layer Heat degree Temp. Pressure Period (kN/m) resistance(Pa) (° C.) (MPa) (min) Max. Min. Avg. (290° C.)

Subduction Ex. 6 1000 295 1 30 0.9 0.7 0.84 Good Good Good Ex. 7 1000295 1 30 0.4 0.3 0.37 Good Good Good Ex. 8 1000 295 4 30 1 0.8 0.95 GoodPoor Poor Com. 1000 295 4 30 0.5 0.3 0.35 Poor Poor Poor Ex. 5

indicates data missing or illegible when filed

As shown in Table 9, in any of Examples, combination of a degassingprocess(es) at the specified condition makes it possible to suppressblister occurrence in the circuit board effectively.

In particular, in the circuit board of Example 6, since the FlatBONDtreatment capable of achieving smooth surface of the copper foil iscarried out in combination with the specific degassing process, theobtained circuit board has not only satisfactory heat resistance butalso improved bonding strength in the circuit board.

It should be noted that in Examples 6 and 7 obtained by lowering thecompression pressure at the time of thermo-compression bonding, it ispossible to reduce the subduction amount into the insulating substrate;and that in Example 8 the circuit board has larger subduction amount ofcircuitry layer in the insulating substrate and is deteriorated in resinflowing because of high pressure in the thermo-compression bonding.

Then, on the basis of Examples 10 to 11 and Comparative Example 6, theeffect of degassing process on the interlayer bonding strength of acircuit board will be considered.

Example 9

A circuit board was produced in the same manner as in Example 4 exceptthat the first degassing was not carried out but the second degassingwas carried out. The obtained circuit board was evaluated in variousphysical properties. Table 10 shows obtained properties.

Example 10

A circuit board was produced in the same manner as in Example 4 exceptthat the first degassing was carried out but the second degassing wasnot carried out. The obtained circuit board was evaluated in variousphysical properties. Table 10 shows obtained properties.

Comparative Example 6

(1) Production of Unit Circuit Board

Onto each surface of a TLCP film having a melting point of 335° C.(“CT-Z”, produced by Kuraray Co., Ltd., thickness: 25 μm), a rolledcopper foil (“BHYX-T-12”, produced by JX Nippon Mining & MetalsCorporation, thickness: 12 μm) was overlaid to obtain a stackedmaterial. The stacked material was placed in a vacuum heat pressapparatus with heated plates at 295° C. under a compression pressure of4 MPa for 10 minutes to be bonded with each other to obtain a firstcopper-clad laminate having a configuration of copper foil/first TLCPfilm/copper foil. In the meantime, onto one surface of a TLCP filmhaving a melting point of 280° C. (“CT-F”, produced by Kuraray Co.,Ltd., thickness: 50 μm), a rolled copper foil (“BHYX-T-12”, produced byJX Nippon Mining & Metals Corporation, thickness: 12 μm) was overlaid toobtain a stacked material. The stacked material was placed in a vacuumheat press apparatus with heated plates at 275° C. under a compressionpressure of 4 MPa for 10 minutes to be bonded with each other to obtaina second copper-clad laminate having a configuration of copperfoil/second TLCP film.

Subsequently, one copper foil of the first copper-clad laminate wasprocessed by a chemical etching process to have a circuit pattern of astrip line structure (existing conductive material ratio: less than 30%)to obtain a first unit circuit board.

Subsequently, a stacked material of the first unit circuit board and thesecond copper-clad laminate, in which the circuit pattern was interposedbetween the first and second TLCP films, was placed in a chamber of avacuum hot press apparatus to be subjected to two-stage press at avacuum degree of 1000 Pa, i.e., first compression-bonding by means ofheated plates set to 150° C. under a compression pressure of 4 MPa for 5minutes (pre-process), followed by second compression-bonding by meansof heated plates set to 320° C. under a compression pressure of 1 MPafor 30 minutes (post-process) to obtain a circuit board having amultilayer configuration of copper foil/first TLCP layer/circuitlayer/second TLCP layer/copper foil. The obtained circuit board wasevaluated in various physical properties. Table 10 shows obtainedproperties.

TABLE 10 Second Circuit board material degassing Second First degassingVacuum First LCP LCP Environ- Temp. Pressure Period degree Temp.Pressure Period film film ment (° C.) (MPa) (min) (Pa) (° C.) (MPa)(min) Ex. 9 CTZ-25 CTF-50 — — — — 1000 100 0 60 (Tm335° C.) (Tm280° C.)Ex. 10 CTZ-25 CTF-50 Ambient 100 0 60 — — — — (Tm335° C.) (Tm280° C.)pressure Com. Ex. 6 CTZ-25 CTF-50 — — — — — — — — (Tm335° C.) (Tm280°C.) Thermo- Bonding strength compression LCP film/LCP CompressionPressure film (kN/m) Temp (° C.) (MPa) Max. Min. Avg. Ex. 9 300 1.0 1.60.7 1.3 Ex. 10 300 1.0 1.1 0.7 0.9 Com. Ex. 6 320 1.0 0.7 0.3 0.5

As shown in Table 10, in Comparative Example 6 without being subjectedto degassing process, bonding strength values are low with respect tonot only the maximum and minimum values but also the average value ofthe whole directions. In particular, Comparative Example 6 hasdifficulty in improvement in bonding strength despite employing highthermo-compression temperature of 320° C. that is intended to increasethe bonding strength. For example, in comparison with Example 4, therepresentative bonding strength value and the minimum bonding strengthvalue of Comparative Example 6 are ⅓ or less and ⅕ or less of Example 4,respectively.

In Example 9, in which the second degassing process was carried out, thebonding strength can be increased in all of the maximum, minimum, andaverage values in comparison with Comparative Example 6. In Example 10,in which the first degassing process was carried out, the bondingstrength can be increased in all of the maximum, minimum, and averagevalues in comparison with Comparative Example 6. In these Examples 9 and10, the bonding strengths of the circuit boards each evaluated from thefour directions can achieve 0.7 kN/m as the minimum value, that is morethan twice of the minimum bonding strength in Comparative Example 6.

INDUSTRIAL APPLICABILITY

The LCP films according to the present invention have satisfactorythermo-adhesive property, and can be advantageously used as variouscircuit board materials. Further, the circuit board of the presentinvention can be used as substrates for various electrical andelectronic products. In particular, since the LCP film has excellentdielectric characteristics at high frequency, the circuit boardaccording to the present invention can be advantageously used as a highfrequency circuit board or the like.

Although the present invention has been fully described in connectionwith the preferred embodiments thereof, those skilled in the art willreadily conceive numerous changes and modifications within the frameworkof obviousness upon the reading of the specification herein presented ofthe present invention. Accordingly, such changes and modifications areto be construed as included therein.

1-17. (canceled)
 18. A method for producing a thermoplastic liquidcrystal polymer film, the method at least comprising: preparing athermoplastic liquid crystal polymer film being capable of forming anoptical anisotropic melt phase and having a segment orientation ratioSOR of 0.8 to 1.4, and degassing the thermoplastic liquid crystalpolymer film by degassing the film (i) under vacuum of 1500 Pa or lowerfor 30 minutes or more, by degassing the film (ii) under heating at atemperature ranging from 100° C. to 200° C., or by degassing the filmunder the above (i) and (ii) simultaneously or separately, so as toproduce a thermoplastic liquid crystal polymer film having a segmentorientation ratio SOR of 0.8 to 1.4 and a moisture content in accordancewith Karl Fischer method of 300 ppm or less.
 19. The method forproducing a thermoplastic liquid crystal polymer film according to claim18, wherein the degassing of the film is performed by a processcomprising: a first degassing of the prepared thermoplastic liquidcrystal polymer film under heating at a temperature ranging from 100° C.to 200° C. for a predetermined period of time, and a second degassing ofthe thermoplastic liquid crystal polymer film after the first degassingunder vacuum of 1500 Pa or lower for a predetermined period of time. 20.The method for producing a thermoplastic liquid crystal polymer filmaccording to claim 18, wherein the degassing under vacuum (i) is carriedout while heating the film at a temperature ranging from 80° C. to 200°C. under vacuum of 1500 Pa or lower.
 21. The method for producing athermoplastic liquid crystal polymer film according to claim 19, whereinthe second degassing process is carried out while heating the film at atemperature ranging from 80° C. to 200° C. under vacuum of 1500 Pa orlower.
 22. The method for producing a thermoplastic liquid crystalpolymer film according to claim 18, wherein the thermoplastic liquidcrystal polymer film has a film thickness of 10 to 200 μm.
 23. Themethod for producing a thermoplastic liquid crystal polymer filmaccording to claim 18, wherein the thermoplastic liquid crystal polymerfilm after degassing has a skin layer.
 24. The method for producing athermoplastic liquid crystal polymer film according to claim 18, whereinthe thermoplastic liquid crystal polymer film after degassing is used asan insulating substrate having a conductor layer on at least onesurface.
 25. The method for producing a thermoplastic liquid crystalpolymer film according to claim 18, wherein the thermoplastic liquidcrystal polymer film after degassing is used as a bonding sheet.
 26. Themethod for producing a thermoplastic liquid crystal polymer filmaccording to claim 18, wherein the thermoplastic liquid crystal polymerfilm after degassing is used as a coverlay.
 27. The method for producinga thermoplastic liquid crystal polymer film according to claim 18,wherein the thermoplastic liquid crystal polymer film to be subjected todegassing is in a sheet form or a roll form.
 28. The method forproducing a thermoplastic liquid crystal polymer film according to claim18, wherein the thermoplastic liquid crystal polymer film to besubjected to degassing is in a roll form having a winding thickness of1000 mm or smaller.
 29. The method for producing a thermoplastic liquidcrystal polymer film according to claim 18, wherein the thermoplasticliquid crystal polymer film after degassing is wrapped with a packagingmaterial having a gas barrier property.
 30. A method for producing acircuit board at least comprising: preparing a plurality of circuitboard materials; stacking the prepared circuit board materials inaccordance with a predetermined structure of a circuit board to obtain astacked material, followed by conducting thermo-compression bonding ofthe stacked material by heating under a predetermined compressionpressure; wherein the prepared circuit board materials are at least onemember selected from the group consisting of an insulating substratehaving an conductor layer on at least one surface, a bonding sheet, anda coverlay, and (I) at least one of the prepared circuit board materialscomprises a degassed thermoplastic liquid crystal polymer film subjectedto degassing as recited in claim 18, (II) at least one of the preparedcircuit board materials comprises a non-degassed thermoplastic liquidcrystal polymer film, and the degassing process as recited in claim 18is conducted after the preparation of the circuit board materials andbefore the thermo-compression bonding, or (III) at least one of theprepared circuit board materials comprises a degassed thermoplasticliquid crystal polymer film subjected to degassing as recited in claim18 and the degassing process as recited in claim 18 is conducted afterthe preparation of the circuit board materials and before thethermo-compression bonding.
 31. The method for producing a circuit boardaccording to claim 30, wherein the thermo-compression bonding of thecircuit board materials is performed by heating the materials whilecompressing the materials under a compression pressure of 5 MPa orlower.
 32. The method for producing a circuit board according to claim31, wherein the thermo-compression bonding of the circuit boardmaterials is performed by heating the materials while compressing thematerials under a compression pressure of 0.5 to 2.5 MPa.
 33. The methodfor producing a circuit board according to claim 30, wherein the circuitboard materials are heated at a temperature ranging from (Tm−60)° C. to(Tm+40)° C. during the thermocompression bonding, where Tm is themelting point of the thermoplastic liquid crystal polymer film subjectedto the thermocompression bonding.